Antireflection film and display device

ABSTRACT

It is an object to provide a high-visibility antireflection film having an antireflection function which can further reduce reflection and a display device that has the antireflection film. A plurality of projections in a pyramidal shape (hereinafter, referred to as pyramidal projection) that are adjacent to each other are provided, and the refractive index of the projection is made to change by the physical pyramidal shape to the outer side (air side) from a surface of a display screen, so that reflection of light is prevented. In addition, the plurality of pyramidal projections are each covered with a film formed of a material having a higher refractive index than the pyramidal projections.

TECHNICAL FIELD

The present invention relates to an antireflection film that has anantireflection function and a display device that has the antireflectionfilm.

BACKGROUND ART

In some display devices having various displays (such as a liquidcrystal display or an electroluminescence display (also referred to asan EL display)), there may be a case where it becomes difficult to see adisplay screen due to reflection of its surroundings by surfacereflection of light from external, so that visibility is decreased. Thisis a considerable problem particularly in an increase in size of thedisplay device and outdoor use thereof.

In order to prevent such reflection of incident light from external, amethod of providing a display screen of a display device with anantireflection film has been employed. For example, there is a method ofproviding an anti-reflective film that has a multilayer structure ofstacked layers having different refractive indices so as to be widelyeffective for a visible light wavelength range (see, for example,Reference 1: Japanese Published Patent Application No. 2003-248102).With a multilayer structure, light rays from external which is reflectedat each interface between the stacked layers interfere and cancel eachother, which provide an antireflection effect.

Further, as an antireflection structure, minute protrusions in a conicalshape or pyramidal shape are arranged over a substrate, and reflectivityat a surface of the substrate is decreased (see, for example, Reference2: Japanese Published Patent Application No. 2004-85831).

DISCLOSURE OF INVENTION

However, with the above-described multilayer structure, a light ray,which cannot be cancelled, of the light rays reflected at the surfacesof each layer is emitted to a viewer side as reflected light. In orderto achieve mutual cancellation of light from external, it is necessaryto precisely control optical characteristics of materials, thicknesses,and the like of films stacked, and it has been difficult to performantireflection treatment to all light rays which are incident fromvarious angles. Further, an antireflection function in theantireflection structure in a conical shape or pyramidal shape has alsobeen insufficient.

In view of the foregoing, a conventional antireflection film has afunctional limitation, and an antireflection film having a higherantireflection function, and a display device having such anantireflection function have been demanded.

It is an object of the present invention to provide a high-visibilitydisplay device with an antireflection function that can further reducereflection of light from external, and a method for manufacturing such adisplay device.

It is a feature of the present invention that a plurality of projectionsin a plyramidal shape (hereinafter, referred to as pyramidalprojections) that are adjacent to each other are provided, and therefractive index of the projection is made to change by the physicalpyramidal shape to the outer side (air side) from a surface of a displayscreen side, so that reflection of light is prevented. In addition, itis also a feature of the present invention that the plurality ofpyramidal projections are each covered with a film formed of a materialhaving a higher refractive index than the pyramidal projections.

In a case where light is incident on a material with a low refractiveindex from a material with a high refractive index, a large differencein refractive index easily causes total reflection of light. Whensurfaces of the pyramidal projections are each covered with a film witha high refractive index, of light going toward the outer side of thepyramidal projections, the amount of light reflected inside thepyramidal projections at interfaces between the films and air isincreased. Furthermore the travelling direction of light inside thepyramidal projections becomes closer to the perpendicular direction to abase due to refraction of light at interfaces between the films and thepyramidal projections, and light is incident on the base (displayscreen); therefore, the number of times of reflection inside thepyramidal projections is decreased. Accordingly, by covering eachpyramidal projection with a film having a high refractive index, thelight confinement effect inside the pyramidal projections is improved,and reflection to the outer side of the pyramidal projections can bereduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented. Since reflection ofincident light from external to the viewer side caused by the flatportions can be reduced, the degree of freedom for selection of shape,setting for arrangement, and a manufacturing process of the pyramidalprojections can be increased.

By stacking a pyramidal projection and a film having a difference inrefractive index therebetween, there is an effect that among lightincident on the film and the pyramidal projection from air, opticalinterfere is generated between reflected light at an interface betweenair and the film and reflected light at an interface between the filmand the pyramidal projection, so that reflected light is reduced.

In the present invention, in the case where the film and the pyramidalprojection have a large difference in reflective index, it is preferablethat the thickness of the film be thin.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like.

By covering the pyramid projection with the film, the physical strengthof the pyramid projection can be enhanced, and reliability is improved.When conductivity is imparted by selecting a material of the film, othereffective functions such as a function of prevention of staticelectricity can be imparted.

According to the present invention, an antireflection film (substrate)that has a plurality of pyramidal projections adjacent to each other anda display device having the antireflection film, can be provided, and ahigh antireflection function can be imparted.

The present invention can be used for a display device that has adisplay function. Examples of display devices that apply the presentinvention include a light-emitting display device having alight-emitting element and a TFT connected together, in which thelight-emitting element includes a layer which contains an organicsubstance, an inorganic substance, or a mixture of an organic substanceand an inorganic substance between a pair of electrodes and whichexhibits light emission called electroluminescence (hereinafter, alsoreferred to as “EL”); a liquid crystal display device which uses aliquid crystal element containing a liquid crystal material as a displayelement; and the like. In the present invention, a “display device”means a device having display elements (e.g., liquid crystal elements orlight-emitting elements). Note that the display device can be a displaypanel in which a plurality of pixels each having a display element suchas a liquid crystal element or an EL element and a peripheral drivercircuit for driving these pixels are formed over a substrate. Further, adisplay device may include a display panel in which ICs, resistors,capacitors, inductors, and transistors are provided to be connected witha flexible printed circuit (FPC) or a printed wiring board (PWB).Furthermore, a display panel may include optical sheets such as apolarizing plate and a retardation plate. In addition, a display panelmay also include a backlight unit (which may include a light guideplate, a prism sheet, a diffusion sheet, a reflection sheet, and a lightsource (e.g., LED or a cold cathode tube)).

Note that a display element and a display device can be in various formsand have various elements. For examples, a display medium whose contrastchanges by an electromagnetic action such as an EL element (an organicEL element, an inorganic EL element, or an EL element containing anorganic substance and an inorganic substance), a liquid crystal element,and electronic ink. Note that display devices using EL elements includean EL display; display devices using liquid crystal elements include aliquid crystal display, a transmissive liquid crystal display, asemi-transmissive liquid crystal display, and a reflective liquidcrystal display; and display devices using electronic ink includeelectronic paper.

One aspect of an antireflection film of the present invention includes aplurality of pyramidal projections that are adjacent to each other withintervals, where the plurality of pyramidal projections are each coveredwith a film, and a refractive index of the film is higher than arefractive index of the pyramidal projection.

Another aspect of an antireflection film of the present inventionincludes a plurality of pyramidal projections, where the plurality ofpyramidal projections are each covered with a film, a refractive indexof the film is higher than a refractive index of the pyramidalprojection, and an interval is provided at least between one side of abase included in a pyramid of one of the pyramidal projections and oneside of a base included in a pyramid of an adjacent pyramidalprojection.

One aspect of a display device of the present invention includes aplurality of pyramidal projections that are adjacent to each other withintervals over a display screen, where the plurality of pyramidalprojections are each covered with a film, and a refractive index of thefilm is higher than a refractive index of the pyramidal projection.

Another aspect of a display device of the present invention includes aplurality of pyramidal projections over a display screen, where theplurality of pyramidal projections are each covered with a film, arefractive index of the film is higher than a refractive index of thepyramidal projection, and an interval is provided at least between oneside of a base included in a pyramid of one of the pyramidal projectionsand one side of a base included in a pyramid of an adjacent pyramidalprojection.

Another aspect of a display device of the present invention includes apair of substrates, at least one of which is a light-transmittingsubstrate, a display element provided between the pair of thesubstrates, and a plurality of pyramidal projections that are adjacentto each other with intervals and provided outside the light-transmittingsubstrate, where the plurality of pyramidal projections are each coveredwith a film, and a refractive index of the film is higher than arefractive index of the pyramidal projection.

Another aspect of a display device of the present invention includes apair of substrates, at least one of which is a light-transmittingsubstrate, a display element provided between the pair of thesubstrates, and a plurality of pyramidal projections provided outsidethe light-transmitting substrate, where the plurality of pyramidalprojections are each covered with a film, a refractive index of the filmis higher than a refractive index of the pyramidal projection, and aninterval is provided at least between one side of a base included in apyramid of one of pyramidal projections and one side of a base includedin a pyramid of an adjacent pyramidal projection.

The pyramidal projection can be formed of not a material having auniform refractive index but a material of a refractive index whichchanges from a surface toward a display screen side. A portion closer toa substrate on the display screen side is formed of a material having arefractive index equivalent to that of the substrate, so that reflectionof light is reduced at an interface between each projection and thesubstrate. The light indicates light that travels inside each projectionand is incident on the substrate.

An antireflection film and a display device of the present inventionhave a plurality of pyramidal projections formed over their surfaces.Light from external which is incident on a pyramidal projection isreflected not to a viewer side but to an adjacent pyramidal projectionbecause the surface of each projection is not flat with respect to thedisplay screen. Incident light from external is partly transmittedthrough each pyramidal projection, whereas reflected light is incidenton the adjacent pyramidal projection. In this manner, light reflected ata surface of a pyramidal projection repeats incidence between adjacentpyramidal projections.

In other words, the number of times of incidence on the antireflectionfilm and the display device among incident light from external isincreased; therefore, the amount of light transmitted through theantireflection film and the display device is increased. Thus, theamount of light reflected to a viewer side is reduced, and the cause ofa reduction in visibility such as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, of light going toward the outer side of the pyramidalprojections, the amount of light reflected inside the pyramidalprojections at interfaces between the films and air is increased.Furthermore, the travelling direction of light inside the pyramidalprojections becomes closer to a direction perpendicular to a base due torefraction of light at interfaces between the films and the pyramidalprojections, and light is incident on the base (display screen);therefore, the number of times of reflection inside the pyramidalprojections is decreased. Accordingly, by covering each pyramidalprojection with a film having a high refractive index, the lightconfinement effect in the pyramidal projections is improved, andreflection to the outer side of the pyramidal projections can bereduced.

Even when the pyramidal projects are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portion can be prevented because reflection to the outerside of the pyramidal projections can be prevented.

By stacking the pyramidal projection and the film having a difference inrefractive index therebetween, there is an effect that among lightincident on the film and the pyramidal projection from air, opticalinterfere is generated between reflected light at an interface betweenair and the film and reflected light at an interface between the filmand the pyramidal projection, so that reflected light is reduced.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced, and reliabilitycan be improved. When the conductivity is imparted by selecting amaterial of the film, other effective function such as a function ofprevention of static electricity can be imparted.

According to the present invention, a high-visibility antireflectionfilm and a display device having the antireflection film can beprovided. The antireflection film has a plurality of pyramidalprojections formed over its surface, and an antireflection function thatcan further reduce reflection of light from external by covering each ofthe plurality of pyramidal projections with a film having a higherrefractive index than the pyramidal projections. Accordingly, a displaydevice having a further high image quality and higher performance can bemanufactured.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C are conceptual views of the present invention.

FIGS. 2A to 2C are conceptual views of the present invention.

FIG. 3A1 to 3C2 are conceptual views of the present invention.

FIG. 4 is a cross-sectional view showing a display device of the presentinvention.

FIG. 5A is a top view showing a display device of the present inventionand

FIGS. 5B and 5C are cross-sectional views thereof.

FIGS. 6A and 6B are cross-sectional views showing a display device ofthe present invention.

FIGS. 7A and 7B are cross-sectional views showing a display device ofthe present invention.

FIG. 8A is a top view showing a display device of the present inventionand FIG. 8B is a cross-sectional view thereof.

FIG. 9A is a top view showing a display device of the present inventionand

FIG. 9B is a cross-sectional view thereof.

FIG. 10 is a cross-sectional view showing a display device of thepresent invention.

FIG. 11 is a cross-sectional view showing a display device of thepresent invention.

FIG. 12 is a cross-sectional view showing a display device of thepresent invention.

FIG. 13 is a cross-sectional view showing a display device of thepresent invention.

FIGS. 14A and 14B are cross-sectional views showing a display module ofthe present invention.

FIG. 15 is a cross-sectional view showing a display module of thepresent invention.

FIGS. 16A to 16D are backlights that can be used as a display device ofthe present invention.

FIGS. 17A to 17C are top views showing a display device of the presentinvention.

FIGS. 18A and 18B are top views showing a display device of the presentinvention.

FIG. 19 is a block diagram showing a main structure of an electronicdevice to which the present invention is applied.

FIGS. 20A and 20B are views showing an electronic device of the presentinvention.

FIGS. 21A to 21F are views each showing an electronic device of thepresent invention.

FIGS. 22A to 22D are cross-sectional views showing a structure of alight-emitting element that can be applied to the present invention.

FIGS. 23A to 23C are cross-sectional views showing a structure of alight-emitting element that can be applied to the present invention.

FIGS. 24A to 24C are cross-sectional views showing a structure of alight-emitting element that can be applied to the present invention.

FIG. 25 is a conceptual view of the present invention.

FIG. 26A is a top view showing a display device of the present inventionand FIG. 26B is a cross-sectional view thereof.

FIGS. 27A and 27B are cross-sectional views showing a conceptual view ofthe present invention.

FIG. 28 is a view showing an experimental model of a comparativeexample.

FIG. 29 is a graph showing an experimental data of Embodiment 1.

FIG. 30 is a photograph showing an experimental data of Embodiment Mode1.

FIG. 31 is a photograph showing an experimental data of EmbodimentModel.

FIGS. 32A to 32C are graphs showing an experimental data of Embodiment1.

FIGS. 33A to 33C are graphs showing an experimental data of Embodiment1.

FIGS. 34A to 34 C are graphs showing an experimental data of Embodiment1.

FIGS. 35A to 35D are views showing a method for manufacturing a film andpyramidal projections of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiment modes of the present invention will be describedwith reference to the accompanying drawings. However, it is easilyunderstood by a person skilled in the art that the present invention canbe carried out in many different modes, and the mode and the detail ofthe present invention can be variously changed without departing fromthe spirit and the scope thereof. Therefore, the present invention isnot interpreted as being limited to the description of the followingembodiment modes. Note that the same reference numeral may be used todenote the same portions or portions having similar functions indifferent diagrams for explaining the structure of the embodiment modeswith reference to drawings, and repetitive explanation thereof isomitted.

Embodiment Mode 1

This embodiment mode will describe an example of an antireflection filmthat has an antireflection function that can further reduce reflectionof light from external, for the purpose of providing excellentvisibility.

FIG. 1A is a top view of an antireflection film of the present inventionand FIGS. 1B and C are cross-sectional views thereof. In FIGS. 1A and1B, a plurality of projections 451 and films 452 are provided over adisplay device 450. FIG. 1A is a top view of a display device of thisembodiment mode. FIG. 1B is a cross-sectional view of FIG. 1A takenalong a line A-B. FIG. 1C is an enlarged view of FIG. 1B. As shown inFIGS. 1A and 1B, the projections 451 are provided to be adjacent to eachother with intervals over a display screen, and there are flat surfaces(surfaces parallel to the display screen) between the projections, withrespect to incident light from external.

In FIG. 1C, a height H1 of a pyramidal projection means a distance froma base to a top of the pyramidal projection. When a height difference dbetween the top of the film and the top of the pyramidal projection isadded to the height H1 of the pyramidal projection, a height H2 thatmeans a height of the pyramidal projection covered with the film can bedetermined. Further, a width L1 is a width of a base of the pyramidalprojection (in this embodiment mode, the pyramidal projection has aconical shape; therefore, a base has a circular shape and L1 is adiameter thereof). When portions of the film in contact with the base ofthe pyramidal projection are added to the width L1 of the pyramidalprojection, a width L2 of the pyramidal projection covered with the filmcan be determined. An angle of an oblique line to the base of thepyramidal projection is an angle θ₁, and an angle of an oblique line tothe base of the pyramidal projection covered with the film is an angleθ₂.

According to the present invention, a plurality of projections in apyramidal shape (hereinafter, referred to as pyramidal projection) thatare adjacent to each other are provided, and the refractive index of theprojection is made to change by a physical shape as a pyramid to theouter side (air side) from a surface of a display screen side, so thatreflection of light is prevented. In addition, the plurality ofpyramidal projections are each covered with a film formed of a materialhaving a higher refractive index than the pyramidal projection.

An antireflection function of a plurality of pyramidal projections inthis embodiment mode of the present invention will be described withreference to FIG. 25. In FIG. 25, pyramidal projections 411 a, 411 b,and 411 c that are adjacent with intervals over a display screen 410 andfilms 414 a, 414 b, and 414 c are shown. When an incident light ray 412a from external is incident on the pyramidal projection 411 c coveredwith the film 414 c, the incident light ray 412 a from external ispartly transmitted to be a transmitted light ray 413 a, and the otherpart of the incident light ray 412 a from external becomes a reflectedlight ray 412 b at a surface of the pyramidal projection 411 c coveredwith the film 414 c to be reflected. The reflected light ray 412 b isincident on the adjacent pyramidal projection 411 b that is covered withthe film 414 b again. The reflected light ray 412 b is partlytransmitted to be a transmitted light ray 413 b, and the other part ofthe reflected light ray 412 b becomes a reflected light ray 412 c at asurface of the pyramidal projection 411 b covered with the film 414 b tobe reflected. The reflected light ray 412 c is incident on the adjacentpyramidal projection 411 c covered with the film 414 c again. Thereflected light ray 412 c is partly transmitted to be a transmittedlight ray 413 c, and the other part of the reflected light ray 412 cbecomes a reflected light ray 412 d at the surface of the pyramidalprojection 411 c covered with the film 414 c to be reflected. Thereflected light ray 412 d is incident on the adjacent pyramidalprojection 411 b covered with the film 414 b again. The reflected lightray 412 d is partly transmitted to be a transmitted light ray 413 d, andthe other part of the reflected light ray 412 d becomes a reflectedlight ray 412 e at the surface of the pyramidal projection 411 b coveredwith the film 414 b to be reflected. Referring to FIG. 25, anantireflection function with the shape of only the pyramidal projectionis described first, and an effect of refraction and reflection of lightat the interface between the films and the pyramidal projections isomitted. However, at the interfaces between the films and the pyramidalprojections, an incident light ray is partly transmitted through theinterfaces to be a transmitted light ray, and the other part of lightray becomes a reflected light ray to be reflected.

As described above, the antireflection film of this embodiment mode hasa plurality of pyramidal projections formed on its surface. Since thesurface of the pyramidal projections is not flat with respect to thedisplay screen, the reflected light ray of the incident light ray is notreflected to the viewer side but reflected to the adjacent pyramidalprojection. The incident light ray is partly transmitted through thepyramidal projection, and the reflected light ray is incident on theadjacent pyramidal projection. In such a manner, the incident light rayfrom external which is reflected at a surface of a pyramidal projectionrepeats incidence on an adjacent pyramidal projection.

That is, since the number of times of light incidence on the pyramidalprojections among light from external is increased, the amount of lighttransmitted through the pyramidal projections is increased. Therefore,the amount of incident light from external which is reflected to theviewer side is reduced, and the cause of a reduction in visibility suchas reflection can be eliminated.

Furthermore, in this embodiment mode, the pyramidal projections are eachcovered with a film having a higher refractive index than the pyramidalprojections. The effect obtained by the film will be explained withreference to FIGS. 27A, 27B, and 28.

FIG. 28 shows a comparative example of a pyramidal projection that isnot covered with a film. An incident light ray 3020 from external entersa pyramidal projection 3023 to be a transmitted light ray 3021 a andtravels inside the pyramidal projection 3023. Part of the transmittedlight ray 3021 a becomes a transmitted light ray 3022 at a surface ofthe pyramidal projection 3023. The transmitted light ray 3022 istransmitted to the outer side of the pyramidal projection 3023. Theother part of the transmitted light ray 3021 a becomes a reflected lightray 3021 b and travels inside the pyramidal projection 3023.

FIG. 27A shows a model to which the present invention is applied, inwhich a light ray 3010 from external is incident on a pyramidalprojection 3001 that is covered with a film 3002. The light ray 3010from external is to be a light ray 3011 traveling inside the film 3002and the pyramidal projection 3001 and a light ray 3012 that is emittedto the outer side of the film 3002 and the pyramidal projection 3001.FIG. 27B shows an enlarged view of a region 3003 of FIG. 27A. In FIG.27B, a light ray 3011 a that is a transmitted light ray of the light ray3010 from external is refracted at an interface between the film 3002and the pyramidal projection 3001 and enters the pyramidal projection3001. Note that the light ray is partly reflected to be a reflectedlight ray at an interface between the film and air, and the other partof the light ray is transmitted to be a transmitted light ray. The lightray 3011 a is refracted at an interface between the film 3002 and thepyramidal projection 3001 to be a light ray 3011 b. The light ray 3011 bis refracted at an interface between the pyramidal projection 3001 andthe film 3002 again to be a light ray 3011 c and incident at aninterface between the film 3002 and air. The light ray 3011 c partlybecomes a transmitted light ray at the interface between the film 3002and air to be emitted outside, and the other part of the light ray 3011c becomes a reflected light ray 3011 d to enter the pyramidal projection3001 again.

Optical calculation for the model of the comparative example in FIG. 28and the model of FIGS. 27A and 27B in this embodiment mode is conducted.A monitor is set in order to count the number of reflected light rays ata surface of the pyramidal projection and the number of light rays thatare leaked to the outer side of the pyramidal projection, and the numberof light rays confined in the conical shape is obtained. FIGS. 30 and 31show results of a light ray tracking simulator, Light Tools(manufactured by Rsoft Design Group, Inc.) based on geometrical optics.FIG. 30 shows the conical projection with a refractive index of 1.35 ina conical shape in the comparative example. FIG. 31 shows a conicalprojection with an refractive index of 1.35 in a conical shape that iscovered with a film made of a material with a refractive index of 1.9.In the comparative example, the pyramidal projection has a height of1500 nm and a width of 150 nm. In the model of FIG. 31 of the presentinvention, although the internal pyramidal projection has a height H1 of1500 nm and a width L1 of 150 nm, when the height and the width of thefilm portion are added, a height H2 of 1540 and a width L2 of 154 nm areobtained.

In the case of only a conical projection as shown in FIG. 30, incidentlight rays (the number of light rays is 500) enter the inner side of thepyramidal projection, and total reflection of the light rays is hardlygenerated at the surface of the conical projection; therefore, the lightrays (the number of the light rays is 468) are emitted to the outside.Light rays transmitted through a plurality of adjacent pyramidalprojections ultimately reach a flat portion, which may become the causefor increase of reflection to the viewer side.

On the other hand, in the case of a surface of the conical projectioncovered with a film as shown in FIG. 31, although incident light rays(the number of light rays is 500) are partly reflected (the number oflight rays is 64) at a surface of the film, the other part of light raysbecome transmitted light rays to travel in the pyramidal projection, andreflection to the inner side of the pyramidal projection is generated atan interface between the film and the outside, whereas light rays areemitted to the outside (the number of light rays is 337). With respectto the number of incident light rays of 500 in the comparative example,although the number of light rays confined in the pyramidal projectionis 32 in the structure of the comparative example of FIG. 30, the numberof light rays confined in the pyramidal projection is 99 in thestructure using the present invention in FIG. 31. Accordingly, it isfound that the film formed of a material with a high refractive indexhas an effect of confining light inside the pyramidal projection.

Further, in the case of a structure of only a conical projection similarto the comparative example (the height of the pyramidal projection is750 nm and the width thereof is 150 nm), in which the refractive indexof the pyramidal projection is 1.492 and the number of incident lightrays is 10000, the number of light rays is 5784 which is transmittedthrough the pyramidal projection and emitted to the outside at aninterface between the pyramidal projection and the outside. On the otherhand, in the case of a structure of a pyramidal projection covered witha film (the pyramidal projection itself has a height H1 of 680 m and awidth L1 of 136 nm; by adding the height and the width of the filmportion, a height H2 is 750 nm and a weight L2 is 150 nm) in which therefractive index of the flm is 1.9, the refractive index of thepyramidal projection is 1.492, and the number of incident light rays is10000, the number of light rays is 4985 which is emitted to the outsideat an interface between the pyramidal projection and the outside.Accordingly, it can be confirmed that the pyramidal projection coveredwith the film having a high refractive index has an effect of confininglight in the pyramidal projection.

In a case where a light ray is incident from a material having a highrefractive index to a material having a low refractive index, if thereis a large difference in a refractive index, total reflection of lightis easily generated. By cocvering a surface of the pyramidal projection3001 with the film 3002 having a high refractive index, among the lightrays emitted to the outer side of the pyramidal projection 3001, theamount of reflected light rays inside the pyramidal projection 3001 atan interface between the film 3002 and air is increased. Further, byrefraction of the light rays at the interface between the film 3002 andthe pyramidal projection 3001, the light rays are incident on a base(display screen) in a condition that the travelling direction of thelight rays in the pyramidal projection 3001 become closer to theperpendicular direction to the base; therefore, the number of reflectionin the pyramidal projection 3001 is reduced. Thus, by covering thepyramidal projection 3001 with the film 3002 having a high refractiveindex, an effect of confining light in the pyramidal projection 3001 isimproved, so that reflection to the outer side of the pyramidalprojection 3001 can be reduced.

Since reflection to the outer side of the pyramidal projection can beprevented, even if the pyramidal projections are adjacent to each otherwith intervals and have flat portions therebetween, light reflection tothe viewer side caused by the flat portions can be prevented. Sincereflection of incident light from external to the viewer side caused bythe flat portions can be reduced, the degree of freedom for selection ofshape, setting for arrangement, and a manufacturing process of thepyramidal projections is increased.

By stacking the pyramidal projection and the film having a difference inrefractive index therebetween, there is an effect that among lightincident on the film and the pyramidal projection from air, opticalinterfere is generated between reflected light at an interface betweenair and the film and reflected light at an interface between the filmand the pyramidal projection, so that reflected light is reduced.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced, and reliability isimproved. When conductivity is imparted by selecting a material of thefilm, other effective functions such as a function of prevention ofstatic electricity can be imparted. As a material that can be used forthe film, conductive titanium oxide having a high light-transmittingproperty for visible light; silicon nitride, silicon oxide, or aluminumoxide having high physical strength; aluminum nitride having high beatconductivity; or the like can be used.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like. Examples of pyramidal projectionshapes are shown in FIGS. 2A to 2C. FIG. 2A shows a pyramidal projection461 that is covered with a film 462 over a display screen 460. Thepyramidal projection 461 covered with the film 462 does not have a shapewhose top is pointed like a normal pyramidal shape but a shape that hasan upper base and a lower base. Therefore, a cross-sectional view thatis taken along a line perpendicular to the base is a trapezoid shape. Inthe present invention, a distance between a lower base and an upper baseis referred to as a height H.

FIG. 2B shows an example in which a pyramidal projection 471 with arounded top is provided over a display device 470 and is covered with afilm 472. In this manner, the pyramidal projection may have a shape witha rounded top and a curvature. In this case, the height H of thepyramidal projection corresponds to a distance between a base and thehighest point of an apex.

FIG. 2C shows an example in which a pyramidal projection 481 having aplurality of angles, θ₁ and θ₂, is provided over a display device 480and is covered with a film 482. In this manner, the pyramidal projectionmay have a shape of a stacked structure of a cylindrical shape and apyramidal shape. In this case, angles made by lateral sides and basesare different as indicated by θ₁ and θ₂. In the case of the pyramidalprojection 481 in FIG. 2C, the height H of the pyramidal projectioncorresponds to the height of the pyramidal shape with oblique lateralsides.

FIGS. 3A to 3C show other examples of shapes and arrangement of aplurality of pyramidal projections covered with films. FIG. 3A2 to 3C2are top views. FIG. 3A1 is a cross-sectional view taken along a line X1to Y1 of FIG. 3A2. FIG. 3B 1 is a cross-sectional view taken along aline X2 to Y2 of FIG. 3B2. FIG. 3C1 is a cross-sectional view takenalong a line X3 to Y3 of FIG. 3C2.

FIGS. 3A1 and 3A2 show an example in which a plurality of pyramidalprojections 466 a to 466 c are adjacent to each other with regularintervals over a display screen of a display device 465 and are coveredwith films 467 a to 467 c, respectively. In such a manner, the pyramidalprojections are not necessarily in contact with each other over thedisplay screen. In the present invention, the pyramidal projectionsprovided with intervals are referred to as an antireflection film (orsubstrate) as a generic term for a portion having an antireflectionfunction. Thus, even when the pyramidal projections are physicallydiscontinuous and are not in a film shape, they are referred to as anantireflection film (or substrate). The pyramidal projections 466 a to466 c each are a quadrangular pyramid whose base is a square.

FIGS. 3B1 and 3B2 show an example in which a plurality of pyramidalprojections 476 a to 476 c are adjacent to each other with intervalsover a display screen of a display device 475 and are covered with films477 a to 477 c, respectively. The pyramidal projections 476 a to 476 ceach have a six-sided pyramid shape whose base is a regular hexagon.

FIGS. 3C1 and 3C2 show an example in which a plurality of pyramidalprojections 486 are provided over a display screen of a display device485 and are covered with films 487 a to 487 c. The plurality ofpyramidal projections 486 may be a single continuous film as shown inFIGS. 3C1 and 3C2, and the pyramidal projections may be provided in anupper part of the surface of the film (substrate).

An antireflection film of the present invention is acceptable as long asit has a pyramidal projection covered with a film. The pyramidalprojection may be directly formed to have a single continuous structureover a surface of a film (substrate). For example, the surface of thefilm (substrate) may be processed to form the pyramidal projection, orthe film (substrate) may be selectively formed to have a pyramidalprojection by a printing method such as nanoimprinting Alternatively,the pyramidal projection may be formed over the film (substrate) inanother step.

FIGS. 35A to 35D show a specific example of a method for formingpyramidal projections covered with a film. In FIGS. 35A to 35D, ananoimprint method is used. A mold-release film 3301 is formed in a mold3300 formed in a pyramidal projection shape, and a thin film 3302 thatis to be a film for covering is formed on the mold-release film 3301.The thin film 3302 is transferred from the mold 3300 to a substrate 3303using the mold-release film 3301 (see FIG. 35A). The thin film 3302 isattached to the substrate 3303, and a thin film 3305 and a mold-releasefilm 3304 each of which has a shape other than a pyramidal projectionshape are transferred to the substrate 3303 (see FIG. 35B).

The mold 3300, a mold-release film 3307, and a thin film 3306 areprinted to a layer 3308 of a pyramidal projection material for imprint,and a pyramidal projection 3309 and films 3310 a, 3310 b, and 3310 c areformed (see FIGS. 35C and 351)). Note that the mold-release film 3301 isnot necessarily required. In a case where the thin film 3306 is formedusing a material capable of being peeled from the mold 3300 easily, themold-release film is not necessary provided.

The thin film 3306 is peeled from the mold 3300 by the mold release film3307 and covers with pyramidal projection 3309 as the films 3310 a, 3310b, and 3310 c.

A plurality of pyramidal projections may be a single continuous film, ora plurality of pyramidal projections may be provided independently overa substrate. Further alternatively, pyramidal projections may be formedon the substrate in advance. As a substrate provided with the pyramidalprojections, a glass substrate, a quartz substrate, or the like can beused. Further, a flexible substrate may be used. The flexible substratemeans a substrate that can be bent, which is formed from, for example, aplastic substrate made of polycarbonate, polyarylate, polyethersulfone,or the like. In addition, a high molecular material, elastomer, can bealso given, which can be processed to be shaped similarly to plastic byplasticization at high temperature, and has a property such as anelastic body like rubber at room temperature. Alternatively, a film(made of polypropylene, polyester, vinyl, polyvinyl fluoride, vinylchloride, or the like), an inorganic film formed by evaporation, or thelike can be used. The plurality of pyramidal projections may be formedon a substrate by processing the substrate, or may be formed over thesubstrate by deposition. Further alternatively, the pyramidalprojections are formed in another step, and then, the pyramidalprojections may be attached to a substrate using an adhesive or thelike. In a case where an antireflection film is provided over a screenof another display device, the pyramidal projections may be attached tothe screen using a binder, an adhesive, or the like. In such a manner,the antireflection film of the present invention can be formed to have aplurality of pyramidal projections having various shapes.

For the film, a material having at least a higher refractive index thana material used for the pyramidal projection may be used. Accordingly, amaterial used for the film is determined relative to a material of asubstrate for partly constituting a display screen of a display deviceand a material of the pyramidal projection formed over the substrate.Therefore, the material used for the film can be determined asappropriate.

Further, the pyramidal projection can be formed of not a material with auniform refractive index but a material of the refractive index whichchanges from the surface to the display screen side. In the plurality ofprojections, a portion that is closer to the substrate side of thedisplay screen is formed of a material with a refractive indexequivalent to that of the substrate to reduce reflection, at aninterface between the projection and the substrate, of light travelinginside each projection and incident on the substrate.

A material used for forming the pyramidal projection and the film may beappropriately selected in accordance with a material of the substratefor partly constituting a display screen surface, such as silicon,nitrogen, fluorine, oxide, nitride, or fluoride. The oxide may besilicon oxide (SiO₂), boric oxide (B₂O₃), sodium oxide (NaO₂), magnesiumoxide (MgO), aluminum oxide (alumina) (Al₂O₃), potassium oxide (K₂O),calcium oxide (CaO), diarsenic trioxide (arsenious oxide) (AS₂O₃),strontium oxide (SrO), antimony oxide (Sb₂O₃), barium oxide (BaO),indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO) inwhich indium oxide is mixed with zinc oxide (ZnO), a conductive materialin which indium oxide is mixed with silicon oxide (SiO₂), organicindium, organic tin, indium oxide containing tungsten oxide, indium zincoxide containing tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, or the like. The nitride maybe aluminum nitride (MN), silicon nitride (SiN), or the like. Thefluoride may be lithium fluoride (LiF), sodium fluoride (NaF), magnesiumfluoride (MgF₂), calcium fluoride (CaF₂), lanthanum fluoride (LaF₃), orthe like. The pyramidal projection and the film may include one or morekinds of the above-mentioned silicon, nitrogen, fluorine, oxide,nitride, and fluoride. A mixing ratio thereof may be appropriately setin accordance with a ratio of components (a composition ratio) of thesubstrate. Further, the materials mentioned as the substrate materialcan also be used.

A plurality of pyramidal projections and films can be formed by forminga thin film by a sputtering method, a vacuum evaporation method, a PVD(physical vapor deposition) method, or a CVD (chemical vapor deposition)method such as a low-pressure CVD (LPCVD) method or a plasma CVD methodand then etching the thin film into a desired shape. Alternatively, adroplet discharge method by which a pattern can be formed selectively, aprinting method by which a pattern can be transferred or drawn (a methodfor forming a pattern such as screen printing or offset printing), acoating method such as a spin coating method, a dipping method, adispenser method, a brush coating method, a spray method, a flow coatingmethod, or the like can be employed. Still alternatively, an imprintingtechnique or a nanoimprinting technique with which a nanoscalethree-dimensional structure can be formed by a transfer technology canbe employed. Imprinting and nanoimprinting are techniques with which aminute three-dimensional structure can be formed without using aphotolithography process.

In this embodiment mode, a high-visibility antireflection film(substrate) and a display device having the antireflection film can beprovided. The antireflection film has a plurality of pyramidalprojection formed over its surface and a high antireflection functionthat can further reduce reflection of incident light from external bycovering each pyramidal projection with a film having a higherrefractive index than the pyramidal projections. Accordingly, a displaydevice with higher image quality and a higher performance can beprovided.

Embodiment Mode 2

This embodiment mode will describe an example of a display device withan antireflection function that can further reduce incident light fromexternal, for the purpose of providing excellent visibility. Morespecifically, an example of a passive-matrix display device will bedescribed.

The display device includes a first electrode layer 751 a, a firstelectrode layer 751 b, and a first electrode layer 751 c which extend ina first direction; an electroluminescent layer 752 which is provided tocover the first electrode layer 751 a, the first electrode layer 751 b,and the first electrode layer 751 c; and a second electrode layer 753 a,a second electrode layer 753 b, and a second electrode layer 753 c whichextend in a second direction perpendicular to the first direction over asubstrate 759 (see FIGS. 5A and 5B). The electroluminescent layer 752 isprovided between the first electrode layer 751 a, the first electrodelayer 751 b, and the first electrode layer 751 c and the secondelectrode layer 753 a, the second electrode layer 753 b, and the secondelectrode layer 753 c. In addition, an insulating layer 754 functioningas a protective film is provided to cover the second electrode layer 753a, the second electrode layer 753 b, and the second electrode layer 753c (see FIGS. 5A and 5B). Further, reference numeral 785 denotes adisplay device. Note that when there is concern about the influence of atransverse electric field between each adjacent light-emitting element,the electroluminescent layer 752 provided in each light-emitting elementmay be separated.

FIG. 5C shows a variation on FIG. 5B, in which a first electrode layer791 a, a first electrode layer 791 b, a first electrode layer 791 c, anelectroluminescent layer 792, a second electrode layer 793 b, and aninsulating layer 794 that is a protective layer are provided over asubstrate 799. Like the first electrode layer 791 a, the first electrodelayer 791 b, and the first electrode layer 791 c in FIG. 5C, the firstelectrode layer may have a tapered shape, in which a radius of curvaturechanges continuously A shape like the first electrode layer 791 a, thefirst electrode layer 791 b, and the first electrode layer 791 c can beformed by a droplet discharge method or the like. When the firstelectrode layer has such a curved surface with a curvature, the coveragethereof by an insulating layer or a conductive layer stacked isfavorable.

In addition, a partition (insulating layer) may be formed to cover anend portion of the first electrode layer. The partition (insulatinglayer) functions like a wall which separates between light-emittingelements. Each of FIGS. 6A and 6B shows a structure in which an endportion of the first electrode layer is covered with a partition(insulating layer).

In one example of a light-emitting element shown in FIG. 6A, a partition(insulating layer) 775 is formed to have a tapered shape to cover endportions of a first electrode layer 771 a, a first electrode layer 771b, and a first electrode layer 771 c. The partition (insulating layer)775 is formed over the first electrode layer 771 a, the first electrodelayer 771 b, and the first electrode layer 771 c which are provided incontact with a substrate 779, and an electroluminescent layer 772, asecond electrode layer 773 b, an insulating layer 774, an insulatinglayer 776 and a substrate 778 are provided.

In one example of a light-emitting element shown in FIG. 6B, a partition(insulating layer) 765 has a shape having a curvature, in which acurvature radius changes continuously. A first electrode layer 761 a, afirst electrode layer 761 b, a first electrode layer 761 c, anelectroluminescent layer 762, a second electrode layer 763 b, aninsulating layer 764, and a protective layer 768 are provided.

FIG. 4 shows a passive-matrix liquid crystal display device to whichthis embodiment mode of the present invention is applied. In FIG. 4, asubstrate 1700 provided with first pixel electrode layers 1701 a, 1701b, and 1701 c, and an insulating layer 1712 functioning as anorientation film faces a substrate 1710 provided with an insulatinglayer 1704 functioning as an orientation film, an opposite electrodelayer 1705, a colored layer 1706 functioning as a color filter, and apolarizing plate 1714, with a liquid crystal layer 1703 interposedtherebetween. Note that reference numeral 1713 denotes a displayelement.

In this embodiment mode, a plurality of pyramidal projections that areadjacent to each other are provided, and a refractive index of theprojection is made to change by physical pyramidal shapes to the outerside (air side) from a surface of a display screen side, so thatreflection of light is prevented. In this embodiment mode, as shown inFIGS. 4 to 6B, pyramidal projections 757, 797, 777, 767, and 1707 areprovided over surfaces of substrates 758, 798, 778, 769, and 1710 on adisplay screen viewer side, respectively. In addition, the plurality ofpyramidal projections 757, 797, 777, 767, and 1707 are covered withfilms 756, 796, 781, 766, and 1708, respectively, that are formed ofmaterials with higher refractive indices than the pyramidal projections757, 797, 777, 767, and 1707.

An antireflection film of the present invention is acceptable as long asthe film has a pyramidal projection covered with a film. The pyramidalprojection may be directly formed to have a single continuous structureover a surface of a film (substrate). For example, the surface of thefilm (substrate) is processed, and the pyramidal projection may beformed thereover, or the film (substrate) may be selectively formed tohave a pyramidal projection by a printing method such as nanoimprintingAlternatively, the pyramidal projection may be formed over the film(substrate) in another step.

The plurality of pyramidal projections may be a single continuous filmor be densely arranged over the substrate. Further alternatively, thepyramidal projections may be formed on the substrate in advance. FIG. 6Ashows an example in which the plurality of pyramidal projections 777 areprovided over a surface of the substrate 778 as a single continuousstructure.

The display device of this embodiment mode has a plurality of pyramidalprojections formed over its surface. Incident light from external isreflected not to a viewer side but to an adjacent pyramidal projectionbecause the surface of each projection is not flat with respect to thedisplay screen. Incident light from external is partly transmittedthrough each pyramidal projection, whereas reflected light is incidenton the adjacent pyramidal projection. In this manner, incident lightfrom external that is reflected by a surface of a pyramidal projectionrepeats incidence between adjacent pyramidal projections.

In other words, the number of times of incidence on the pyramidalprojections among incident light from external is increased; therefore,the amount of light transmitted through the pyramidal projections isincreased. Thus, the amount of light from external that is reflected toa viewer side is reduced, and the cause of reduction in visibility suchas reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomesclose to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projections, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside of the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect inside the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented. Since reflection ofincident light from external to the viewer side caused by the flatportions can be reduced, the degree of freedom for selection of shape,setting for arrangement, and a manufacturing process of the pyramidalprojections can be increased.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface of air and the film and reflected lightat an interface between the film and the pyramidal projection, so thatreflected light is reduced.

In the present invention, in the case where the film and the pyramidalprojection have a large difference in reflective index, it is preferablethat the thickness of the film be thin.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved. Even in a case of a structurein which flat portions are provided between the pyramidal projectionslike a conical shape, light incident on the flat portions is reduced dueto the light confinement effect inside the pyramidal projection by thefilm, and reflection to the viewer side can be further prevented.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced, and reliability isimproved. When conductivity is imparted by selecting a material of thefilm, other effective functions such as a function of prevention ofstatic electricity can be imparted. As a material that can be used forthe film, conductive titanium oxide having a high light-transmittingproperty in visible light; silicon nitride, silicon oxide, or aluminumoxide having high physical strength; aluminum nitride having high heatconductivity; or the like can be used.

The plurality of pyramidal projections 757, 797, 777, 767, and 1707 ofthis embodiment mode are provided with regular intervals between a topof one pyramidal projection and a top of the adjacent pyramidalprojection. Therefore, each projection is an isosceles triangle in across section.

For the film, a material with a higher refractive index than at least amaterial used for the pyramidal projection may be used. Accordingly, amaterial used for the film is determined relative to a material of asubstrate for partly constituting a display screen of a display deviceand a material of the pyramidal projection formed over the substrate.Therefore, the material used for the film can be determined asappropriate. A material used for forming the pyramidal projection andthe film may be appropriately selected in accordance with a material ofthe substrate forming a display screen surface, such as silicon,nitrogen, fluorine, oxide, nitride, or fluoride. The oxide may besilicon oxide (SiO₂), boric oxide (B₂O₃), sodium oxide (NaO₂), magnesiumoxide (MgO), aluminum oxide (alumina) (Al₂O₃), potassium oxide (K₂O),calcium oxide (CaO), diarsenic trioxide (arsenious oxide) (As₂O₃),strontium oxide (SrO), antimony oxide (Sb₂O₃), barium oxide (BaO),indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO) inwhich indium oxide is mixed with zinc oxide (ZnO)₇ a conductive materialin which indium oxide is mixed with silicon oxide (SiO₂), organicindium, organic tin, indium oxide containing tungsten oxide, indium zincoxide containing tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, or the like. The nitride maybe aluminum nitride (AlN), silicon nitride (SiN), or the like. Thefluoride may be lithium fluoride (LiF), sodium fluoride (NaF), magnesiumfluoride (MgF₂), calcium fluoride (CaF₂), lanthanum fluoride (LaF₃), orthe like. The pyramidal projection and the film may include one or morekinds of the above-mentioned silicon, nitrogen, fluorine, oxide,nitride, and fluoride. A mixing ratio thereof may be appropriately setin accordance with a ratio of components (a composition ratio) of thesubstrate.

A plurality of pyramidal projections and films can be formed by forminga thin film by a sputtering method, a vacuum evaporation method, a PVD(physical vapor deposition) method, or a CVD (chemical vapor deposition)method such as a low-pressure CVD (LPCVD) method or a plasma CVD methodand then etching the thin film into a desired shape. Alternatively, adroplet discharge method by which a pattern can be formed selectively, aprinting method by which a pattern can be transferred or drawn (a methodfor forming a pattern such as screen printing or offset printing), acoating method such as a spin coating method, a dipping method, adispenser method, a brush coating method, a spray method, a flow coatingmethod, or the like can be employed. Still alternatively, an imprintingtechnique or a nanoimprinting technique with which a nanoscalethree-dimensional structure can be formed by a transfer technology canbe employed. Imprinting and nanoimprinting are techniques with which aminute three-dimensional structure can be formed without using aphotolithography process.

As the substrates 758, 759, 769, 778, 779, 798, 799, 1700, and 1710, aglass substrate, a quartz substrate, or the like can be used. Further, aflexible substrate may be used. The flexible substrate means a substratethat can be folded, which is formed from, for example, a plasticsubstrate made of polycarbonate, polyarylate, polyethersulfone, or thelike. In addition, a high molecular material, elastomer, can be alsogiven, which can be processed for shaping similarly to plastic by beingplasticization at high temperature, and has a property such as anelastic body like rubber at room temperature. Alternatively, a film(made of polypropylene, polyester, vinyl, polyvinyl fluoride, vinylchloride, or the like), an inorganic film formed by evaporation, or thelike can be used.

The partition (insulating layer) 765 and the partition (insulatinglayer) 775 may be formed using an inorganic insulating material such assilicon oxide, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, or aluminum oxynitride; an acrylic acid, a methacrylicacid, or a derivative thereof; a heat-resistant high molecular compoundsuch as polyimide, aromatic polyamide, or polybenzimidazole; or asiloxane resin. Alternatively, a resin material such as a vinyl resinlike polyvinyl alcohol or polyvinylbutyral, an epoxy resin, a phenolresin, a novolac resin, an acrylic resin, a melamine resin, or aurethane resin may be used. Further, an organic material such asbenzocyclobutene, parylene, fluorinated arylene ether, or polyimide, acomposition material containing a water-soluble homopolymer and awater-soluble copolymer, or the like may be used. The partition(insulating layer) 765 and the partition (insulating layer) 775 can beformed by a vapor-phase growth method such as a plasma CVD method or athermal CVD method, or a sputtering method. Alternatively, they can beformed by a droplet discharge method or a printing method (such asscreen printing or offset printing by which a pattern is formed). A filmobtained by a coating method, an SOG film, or the like can also be used.

After forming a conductive layer, an insulating layer, or the like bydischarging a composition by a droplet discharge method, a surfacethereof may be planarized by pressing with pressure to improveplanarity. As a pressing method, unevenness may be reduced by moving aroller-shaped object over the surface, or the surface may be pressedwith a flat plate-shaped object. A heating step may be performed at thetime of pressing. Alternatively, surface unevenness may be eliminatedwith an air knife after softening or melting the surface with a solventor the like. A CMP method may be alternatively used for polishing thesurface. This step may be employed in planarizing the surface whenunevenness is generated by a droplet discharge method.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering each pyramidal projection with a film having ahigher refractive index than the pyramidal projections. Accordingly, adisplay device with higher image quality and a higher performance can beprovided.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 3

This embodiment mode describes an example of a display device having anantireflection function that can further reduce reflection of light fromexternal, for the purpose of providing excellent visibility. Thisembodiment mode describes a display device having a different structurefrom that of Embodiment Mode 2. Specifically, this embodiment modedescribes a case where the display device has an active-matrixstructure.

FIG. 26A is a top view of the display device, and FIG. 26B is across-sectional view of FIG. 26A taken along a line E-F. Although anelectroluminescent layer 532, a second electrode layer 533, and aninsulating layer 534 are omitted and not shown in FIG. 26A, each of themis provided as shown in FIG. 26B.

First wirings that extend in a first direction and second wirings thatextend in a second direction perpendicular to the first direction areprovided in matrix over a substrate 520 provided with an insulatinglayer 523 as a base film. One of the first wirings is connected to asource electrode or a drain electrode of a transistor 521, and one ofthe second wirings is connected to a gate electrode of the transistor521. A first electrode layer 531 is connected to a wiring layer 525 bthat is the source electrode or the drain electrode of the transistor521, which is not connected to the first wiring, and a light-emittingelement 530 is formed using a stacked structure of the first electrodelayer 531, the electroluminescent layer 532, and the second electrodelayer 533. A partition (insulating layer) 528 is provided betweenadjacent light-emitting elements, and the electroluminescent layer 532and the second electrode layer 533 are stacked over the first electrodelayer and the partition (insulating layer) 528. An insulating layer 534functioning as a protective layer and a substrate 538 functioning as asealing substrate are provided over the second electrode layer 533. Asthe transistor 521, an inversed staggered thin film transistor is used(see FIGS. 26A and 26B). Light which is emitted from the light-emittingelement 530 is extracted from the substrate 538 side. Thus, a surface ofthe substrate 538 to a viewer side is provided with a plurality ofpyramidal projections 529 of this embodiment mode and films 536 withwhich the pyramidal projections 529 are covered.

FIGS. 26A and 26B in this embodiment mode show an example in which thetransistor 521 is a channel-etch inversed-staggered transistor. In FIGS.26A and 26B, the transistor 521 includes a gate electrode layer 502, agate insulating layer 526, a semiconductor layer 504, semiconductorlayers 503 a and 503 b having one conductivity type, wiring layers 525 aand 525 b, one of which serves as a source electrode layer and the otheras a drain electrode layer.

The semiconductor layer can be formed using the following material: anamorphous semiconductor (hereinafter also referred to as an “AS”)manufactured by a vapor-phase growth method using a semiconductormaterial gas typified by silane or germane or a sputtering method; apolycrystalline semiconductor that is formed by crystallizing theamorphous semiconductor by utilizing light energy or thermal energy; asemiamorphous (also referred to as microcrystalline or microcrystal)semiconductor (hereinafter also referred to as a “SAS”); or the like.

The SAS is a semiconductor having an intermediate structure between anamorphous structure and a crystalline structure (including a singlecrystal and a polycrystal) and having a third state which is stable interms of free energy, and includes a crystalline region havingshort-range order and lattice distortion. The SAS is formed by glowdischarge decomposition (plasma CVD) of a gas containing silicon. SiH₄is used as the gas containing silicon. Alternatively, Si₂H₆, SiH₂Cl₂,SiHCl₃, SiCl₄, SiF₄, or the like can be used. Further, F₂ or GeF₄ may bemixed. This gas containing silicon may be diluted with H₂, or H₂ and oneor more rare gas elements of He, Ar, Kr, and Ne. By further promotion oflattice distortion by inclusion of a noble gas element such as helium,argon, crypton, or neon, a favorable SAS with its stability increasedcan be obtained. The semiconductor layer may be formed by stacking anSAS layer formed from a fluorine-based gas and an SAS layer formed froma hydrogen-based gas.

The amorphous semiconductor is typified by hydrogenated amorphoussilicon, and the crystalline semiconductor is typified by polysilicon orthe like. Polysilicon (polycrystalline silicon) includes so-calledhigh-temperature polysilicon which contains polysilicon formed at aprocess temperature of 800° C. or higher as the main component,so-called low-temperature polysilicon which contains polysiticon formedat a process temperature of 600° C. or lower as the main component, andpolysilicon crystallized by adding an element which promotescrystallization or the like. Naturally, as described above, asemiamorphous semiconductor, or a semiconductor which includes acrystalline phase in a portion of a semiconductor layer can be used.

In a case where a crystalline semiconductor layer is used as thesemiconductor layer, the crystalline semiconductor layer may bemanufactured by using a known method (a laser crystallization method, athermal crystallization method, a thermal crystallization method usingan element which promotes crystallization such as nickel, or the like).A microcrystalline semiconductor, which is a SAS, can be crystallized bylaser irradiation to improve crystallinity. In a case where the elementwhich promotes crystallization is not introduced, hydrogen is releaseduntil a concentration of hydrogen contained in an amorphous silicon filmbecomes 1×10²⁰ atoms/cm³ or less by heating the amorphous silicon layerat a temperature of 500° C. for one hour in a nitrogen atmosphere beforeirradiating the amorphous silicon layer with laser light. This isbecause the amorphous silicon film containing much hydrogen is damagedwhen irradiated with laser light. The heat treatment for crystallizationcan be performed using a heating furnace, laser irradiation, irradiationwith light emitted from a lamp (also referred to as lamp annealing), orthe like. An example of a heating method is an RTA method such as a GRTA(gas rapid thermal annealing) method or an LRTA (lamp rapid thermalannealing) method, GRTA is a method for performing heat treatment usinga high-temperature gas, and LRTA is a method for performing heattreatment by lamp light.

The crystallization may be performed by adding an element which promotescrystallization (also referred to as a catalyst element or a metalelement) to the amorphous semiconductor layer and performing heattreatment (at 550° C. to 750° C. for 3 minutes to 24 hours) in acrystallization step in which an amorphous semiconductor layer iscrystallized to form a crystalline semiconductor layer. As the elementwhich promotes crystallization, one or more elements of iron (Fe),nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd),osmium (Os), iridium (Ir), platinum (Pt), copper (Cu), and gold (Au) canbe used.

Any method can be used to introduce a metal element into the amorphoussemiconductor layer as long as the method is capable of making the metalelement exist on the surface of or inside of the amorphous semiconductorlayer. For example, a sputtering method, a CVD method, a plasmatreatment method (including a plasma CVD method), an adsorption method,or a method in which a metal salt solution is applied can be employed.Among them, the method using a solution is simple and easy, andadvantageous in terms of easy concentration control of the metalelement. It is preferable to form an oxide film by irradiation with UVlight in an oxygen atmosphere, a thermal oxidation method, a treatmentwith ozone water or hydrogen peroxide including a hydroxyl radical, orthe like in order to improve wettability of the surface of the amorphoussemiconductor layer to spread an aqueous solution over the entiresurface of the amorphous semiconductor film.

In order to remove the element which promotes crystallization from thecrystalline semiconductor layer or reduce the element, a semiconductorlayer containing an impurity element is formed in contact with thecrystalline semiconductor layer, which functions as a gettering sink.The impurity element may be an impurity element imparting n-typeconductivity, an impurity element imparting p-type conductivity, a noblegas element, or the like. For example, one or more elements ofphosphorus (P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi),boron (B), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon(Xe) can be used. A semiconductor layer containing a noble gas elementis formed in contact with the crystalline semiconductor layer containingthe element which promotes crystallization, and heat treatment (at 550°C. to 750° C. for 3 minutes to 24 hours) is performed. The element whichpromotes crystallization in the crystalline semiconductor layer movesinto the semiconductor layer containing a noble gas element; thus, theelement which promotes crystallization in the crystalline semiconductorlayer is removed or reduced. After that, the semiconductor layercontaining a noble gas element, which serves as a gettering sink, isremoved.

Laser irradiation can be performed by relatively moving a laser beam andthe semiconductor layer. In laser irradiation, a marker can also beformed in order to overlap a beam with high accuracy or control a startposition or an end position of laser irradiation. The marker may beformed over the substrate at the same time as the formation of theamorphous semiconductor film.

In a case of using laser irradiation, a continuous-wave laser beam (CWlaser beam) or a pulsed laser beam can be used. An applicable laser beamis a beam emitted from one or more kinds of the following lasers: a gaslaser such as an Ar laser, a Kr laser, or an excimer laser; a laserusing, as a medium, single-crystalline YAG, YVO₄, forsterite (Mg₂SiO₄),YAlO₃, or GdVO₄, or polycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, orGdVO₄, to which one or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta isadded as a dopant; a glass laser; a ruby laser; an alexandrite laser; aTi:sapphire laser; a copper vapor laser; and a gold vapor laser. Acrystal having a large grain diameter can be obtained by irradiationwith the fundamental wave of the above laser beam or the second harmonicto the fourth harmonic of the fundamental wave thereof. For example, thesecond harmonic (532 nm) or the third harmonic (355 nm) of a Nd:YVO₄laser (the fundamental wave: 1064 nm) can be used. This laser can emiteither a CW laser beam or a pulsed laser beam. When the laser emits a CWlaser beam, a power density of the laser needs to be about 0.01 MW/cm²to 100 MW/cm² (preferably, 0.1 MW/cm² to 10 MW/cm²). A scanning rate isset to be about 10 cm/sec to 2000 cm/sec for irradiation.

Note that the laser using, as a medium, single-crystalline YAG, YVO₄,forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄, or polycrystalline (ceramic) YAG,Y₂O₃, YVO₄, YAlO₃, or GdVO₄, to which one or more of Nd, Yb, Cr, Ti, Ho,Er, Tm, and Ta is added as a dopant; an Ar ion laser; or a Ti:sapphirelaser can be a CW laser. Alternatively, it can be pulsed at a repetitionrate of 10 MHz or more by performing Q-switching operation, modelocking, or the like. When a laser beam is pulsed at a repetition rateof 10 MHz or more, the semiconductor layer is irradiated with a pulsedlaser beam after being melted by a preceding laser beam and before beingsolidified. Therefore, unlike a case of using a pulsed laser having alow repetition rate, the interface between the solid phase and theliquid phase can be moved continuously in the semiconductor layer, sothat crystal grains grown continuously in the scanning direction can beobtained.

When ceramic (polycrystal) is used as a medium, the medium can be formedinto a desired shape in a short time at low cost. In the case of using asingle crystal, a columnar medium having a diameter of severalmillimeters and a length of several tens of millimeters is generallyused. However, in the case of using ceramic, a larger medium can beformed.

A concentration of a dopant such as Nd or Yb in a medium, which directlycontributes to light emission, cannot be changed largely either in asingle crystal or a polycrystal. Therefore, there is limitation to someextent on improvement in laser output by increasing the concentration.However, in the case of using ceramic, the size of the medium can besignificantly increased compared with the case of using a singlecrystal, and thus, significant improvement in output can be achieved.

Furthermore, in the case of using ceramic, a medium having aparallelepiped shape or a rectangular solid shape can be easily formed.When a medium having such a shape is used and emitted light propagatesinside the medium in zigzag, an emitted light path can be extended.Therefore, the light is amplified largely and can be emitted with highoutput. In addition, since a laser beam emitted from a medium havingsuch a shape has a quadrangular shape in cross-section at the time ofemission, it has an advantage over a circular beam in being shaped intoa linear beam. By shaping the laser beam emitted as described aboveusing an optical system, a linear beam having a length of 1 mm or lesson a shorter side and a length of several millimeters to several meterson a longer side can be easily obtained. Further, by uniformlyirradiating the medium with excited light, the linear beam has a uniformenergy distribution in a long-side direction. Moreover, thesemiconductor layer is preferably irradiated with the laser beam at anincident angle θ (0°<θ<90°) because laser interference can be prevented.

By irradiating the semiconductor layer with this linear beam, the entiresurface of the semiconductor layer can be annealed more uniformly. Whenuniform annealing is needed to both ends of the linear beam, a device ofproviding slits at the both ends so as to shield a portion where energyis decayed, or the like against light is necessary.

When the linear beam with uniform intensity, which is obtained asdescribed above, is used for annealing the semiconductor layer and adisplay device is manufactured using this semiconductor layer, thedisplay device has favorable and uniform characteristics.

The laser light irradiation may be performed in an inert gas atmospheresuch as in a rare gas or nitrogen. This can suppress surface roughnessof the semiconductor layer due to laser light irradiation and variationof threshold value which is caused by variation of interface statedensity.

The amorphous semiconductor layer may be crystallized by a combinationof heat treatment and laser light irradiation, or several times of heattreatment or laser light irradiation alone.

The gate electrode layer can be formed by a sputtering method, anevaporation method, a CVD method, or the like. The gate electrode layermay be formed using an element such as tantalum (Ta), tungsten (W),titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu), chromium(Cr), or neodymium (Nd) or an alloy or compound material containing theelement as its main component. Alternatively, the gate electrode layermay be formed using a semiconductor film typified by a polycrystallinesilicon film doped with an impurity element such as phosphorus, or anAgPdCu alloy. The gate electrode layer may be a single layer or stackedlayers.

Although the gate electrode layer is formed in a tapered shape in thisembodiment mode, the present invention is not limited thereto. The gateelectrode layer may have a stacked structure, in which only one layermay have a tapered shape and the other layer may have a perpendicularside surface by anisotropic etching. The gate electrode layers stackedmay have different taper angles or the same taper angle. When the gateelectrode layer has a tapered shape, the coverage thereof with a film tobe stacked thereover is improved, and defects can be reduced.Accordingly, reliability is improved.

The source electrode layer or the drain electrode layer can be formed byforming a conductive film by a PVD method, a CVD method, an evaporationmethod, or the like and then etching the conductive film into a desiredshape. Alternatively, a conductive layer can be selectively formed in adesired position by a droplet discharge method, a printing method, adispenser method, an electroplating method, or the like. Stillalternatively, a reflow method or a damascene method may be used. Thesource electrode layer or the drain electrode layer can be formed usinga conductive material such as a metal, specifically, an element such asAg, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba,Si, or Ge, or an alloy or a nitride thereof. Alternatively, a stackedstructure thereof may be used.

The insulating layers 523, 526, 527, and 534 may be formed using aninorganic insulating material such as silicon oxide, silicon nitride,silicon oxynitride, aluminum oxide, aluminum nitride, or aluminumoxynitride; an acrylic acid, a methacrylic acid, or a derivativethereof; a heat resistant high molecular compound such as polyimide,aromatic polyamide, or polybenzimidazole; or a sitoxane resin.Alternatively, a resin material such as a vinyl resin like polyvinylalcohol or polyvinylbutyral, an epoxy resin, a phenol resin, a novolacresin, an acrylic resin, a melainine resin, or a urethane resin may beused. Further, an organic material such as benzocyclobutene, fluorinatedarylene ether, or polyimide, a composition material containing awater-soluble homopolymer and a water-soluble copolymer, or the like maybe used. The insulating layers 523, 526, 527, and 534 can be formed by avapor-phase growth method such as a plasma CVD method or a thermal CVDmethod, or a sputtering method. Alternatively, they can be formed by adroplet discharge method or a printing method (such as screen printingor offset printing by which a pattern is formed). A film obtained by acoating method, an SOG film, or the like can also be used.

Without limitation to this embodiment mode, the thin film transistor mayhave a single-gate structure in which a single channel formation regionis formed, a double-gate structure in which two channel formationregions are formed, or a triple-gate structure in which three channelformation regions are formed. In addition, a thin film transistor in aperipheral driver circuit region may also have a single-gate structure,a double-gate structure, or a triple-gate structure.

Note that without limitation to the manufacturing method of a thin filmtransistor described in this embodiment mode, the present invention canbe used in a top-gate structure (such as a staggered structure or acoplanar structure), a bottom-gate structure (such as an invertedcoplanar structure), a dual-gate structure including two gate electrodelayers provided above and below a channel region each with a gateinsulating film interposed therebetween, or other structures.

Each of FIGS. 7A and 7B shows an active-matrix liquid crystal displaydevice to which this embodiment mode of the present invention isapplied. In each of FIGS. 7A and 7B, a substrate 550 provided with atransistor 551 having a multi-gate structure, a pixel electrode layer560, and an insulating layer 561 functioning as an orientation filmfaces a substrate 568 provided with an insulating layer 563 functioningas an orientation film, a conductive layer 564 functioning as anopposite electrode layer, a colored layer 565 functioning as a colorfilter, and a polarizer (also referred to as a polarizing plate) 556,with a liquid crystal layer 562 interposed therebetween. A surface ofthe substrate 568 to a viewer side is provided with a plurality ofpyramidal projections 567 and films 566 with which the pyramidalprojections 567 are covered of this embodiment mode.

A transistor 551 is a channel-etch inversed-staggered transistor havinga multi-gate structure. In FIG. 7A, the transistor 551 includes gateelectrode layers 552 a and 552 b, a gate insulating layer 558, asemiconductor layer 554, semiconductor layers imparting one conductivitytype 553 a, 553 b, and 553 c, and wirings 555 a, 555 b, and 555 c to bea source electrode layer and a drain electrode layer. An insulatinglayer 557 is provided over the transistor 551.

The display device of FIG. 7A is an example in which the plurality ofpyramidal projections 567 are provided on an outer side of the substrate568 and the polarizer 556, the colored layer 565, and the conductivelayer 564 are sequentially provided on an inner side. However, thepolarizer 569 may be provided on the outer side of the substrate 568 (toa viewer side) as shown in FIG. 7B, and in that case, the plurality ofpyramidal projections 567 may be provided over a surface of thepolarizer 569. The stacked structure of the polarizer and the coloredlayer is also not limited to that of FIG. 7A and may be appropriatelydetermined depending on materials of the polarizer and the colored layeror conditions of a manufacturing process.

FIG. 13 shows active-matrix electronic paper of this embodiment mode towhich the present invention is applied. Although FIG. 13 shows anactive-matrix structure, the present invention can also be applied to apassive-matrix structure.

Although each of FIGS. 7A and 7B shows a liquid crystal display elementas an example of a display element, a display device using a twistingball display system may be used. A twisting ball display system is amethod in which display is performed by arranging spherical particleseach of which is colored separately in black and white between a firstelectrode layer and a second electrode layer, and generating a potentialdifference between the first electrode layer and the second electrodelayer so as to control the directions of the spherical particles.

A transistor 581 is an inverted coplanar thin film transistor, whichincludes a gate electrode layer 582, a gate insulating layer 584, wiringlayers 585 a and 585 b, and a semiconductor layer 586. In addition, thewiring layer 585 b is electrically connected to the first electrodelayers 587 a and 587 b through an opening formed in an insulating layer598. Between the first electrode layers 587 a and 587 b, and a secondelectrode layer 588, spherical particles 589, each of which includes ablack region 590 a and a white region 590 b, and a cavity 594 which isfilled with liquid around the black region 590 a and the white region590 b, are provided. A space around the spherical particle 589 is filledwith a filler 595 such as a resin (see FIG. 13). A surface of asubstrate 599 to a viewer side is provided with a plurality of pyramidalprojections 597 and films 596 with which the pyramidal projections 597are covered of this embodiment mode.

Instead of the twisting ball, an electrophoretic element can also beused. A microcapsule having a diameter of approximately 10 μm to 20 μm,in which a transparent liquid, and positively charged whitemicroparticles and negatively charged black microparticles areencapsulated, is used. In the microcapsule which is provided between thefirst electrode layer and the second electrode layer, when an electricfield is applied by the first electrode layer and the second electrodelayer, the white microparticles and the black microparticles migrate toopposite sides to each other, so that white or black can be displayed. Adisplay element using this principle is an electrophoretic displayelement, and is called electronic paper in general. The electrophoreticdisplay element has higher reflectance than a liquid crystal displayelement, and thus, an auxiliary light is unnecessary, less power isconsumed, and a display portion can be recognized in a dusky place. Evenwhen power is not supplied to the display portion, an image which hasbeen displayed once can be maintained. Thus, it is possible that adisplayed image can be stored, even if a semiconductor device having adisplay function is distanced from a source of an electric wave.

The transistor may have any structure, as long as the transistor canserve as a switching element. The semiconductor layer may be formedusing various semiconductors such as an amorphous semiconductor, acrystalline semiconductor, a polycrystalline semiconductor, and amicrocrystalline semiconductor, or an organic transistor may be formedusing an organic compound.

In this embodiment mode, a plurality of pyramidal projections that areadjacent to each other are provided, and a refractive index of theprojection is made to change by a physical pyramidal shape to the outerside (air side) from a surface of a display screen side, so thatreflection of light is prevented. In this embodiment mode, as shown inFIGS. 7A and 7B, FIG. 13, and FIGS. 26A and 26B, the pyramidalprojections 567, 597, and 529 are provided over the surfaces of thesubstrates 568, 599, and 538 on the surfaces of the display screen side.In addition, the plurality of pyramidal projections 567, 597, and 529are covered with the films 566, 596, and 536, respectively, formed ofmaterials with higher refractive indices than those of the pyramidalprojections 567, 597, and 529.

A display device of the present invention is acceptable as long as ithas a pyramidal projection covered with a film. The pyramidal projectionmay be directly formed to have a single continuous structure over asurface of a film (substrate). For example, the surface of the film(substrate) is processed, and the pyramidal projection may be formedthereover, or the film (substrate) may be selectively formed to have apyramidal projection by a printing method such as nanoimprinting.Alternatively, the pyramidal projection may be formed over the film(substrate) in another step.

The plurality of pyramidal projections may be a single continuous filmor be independently arranged over the substrate.

The display device of this embodiment mode includes a plurality ofpyramidal projections formed over its surface. Light from external isreflected not to a viewer side but to an adjacent pyramidal projectionbecause the surface of each projection is not flat with respect to thedisplay screen. Incident light from external is partly transmittedthrough each pyramidal projection, whereas reflected light is incidenton an adjacent pyramidal projection. In this manner, light reflected ata surface of a pyramidal projection repeats incidence between adjacentpyramidal projections.

In other words, the number of times of incidence on the pyramidalprojections among light from external is increased; therefore, theamount of light transmitted through the pyramidal projections isincreased. Thus, the amount of light from external which is reflected toa viewer side is reduced, and the cause of a reduction in visibilitysuch as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomesclose to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projections, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervas and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portion can be prevented because reflection to the outerside of the pyramidal projections can be prevented. Since reflection ofincident light from external to the viewer side caused by the flatportion can be reduced, the degree of freedom for selection of shape,setting for arrangement, and a manufacturing process of the pyramidalprojections can be increased.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and the pyramidal projection from air, optical interfere isgenerated between reflected light at an interface between air and thefilm and reflected light at an interface between the film and thepyramidal projection, so that reflected light is reduced.

In the present invention, in the case where the film and the pyramidalprojection have a large difference in reflactive index, it is preferablethat the thickness of the film be thin.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved. Even in a case of a structurein which flat portions are peovided between the pyramidal projectionslike a conical shape, light incident on the flat portions is reduced dueto the light confinement effect inside the pyramidal projection by thefilm, and reflection to the viewer side can be further prevented.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced, and reliability isimproved. When conductivity is imparted by selecting a material of thefilm, other effective functions such as a function of prevention ofstatic electricity can be imparted. As a material that can be used forthe film, conductive titanium oxide having a high light-transmittingproperty in visible light; silicon nitride, silicon oxide, or aluminumoxide having high physical strength; aluminum nitride having high heatconductivity; or the like can be used.

For the film, a material with a higher refractive index than at least amaterial used for the pyramidal projection may be used. Accordingly, amaterial used for the film is determined relative to a material of asubstrate for partly constituting a display screen of a display deviceand a material of the pyramidal projection formed over the substrate.Therefore, the material used for the film can be determined asappropriate.

A material used for forming the pyramidal projection and the film may beappropriately selected in accordance with a material of the substrateforming a display screen surface, such as silicon, nitrogen, fluorine,oxide, nitride, or fluoride. The oxide may be silicon oxide (SiO₂),boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO), aluminumoxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide (CaO),diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide (SrO),antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide (ITO), zincoxide (ZnO), indium zinc oxide (IZO) in which indium oxide is mixed withzinc oxide (ZnO), a conductive material in which indium oxide is mixedwith silicon oxide (SiO₂), organic indium, organic tin, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, or the like. The nitride may be aluminum nitride (AlN),silicon nitride (SiN), or the like. The fluoride may be lithium fluoride(LiF), sodium fluoride (NaF), magnesium fluoride (MgF₂), calciumfluoride (CaF₂), lanthanum fluoride (LaF₃), or the like. The pyramidalprojection and the film may include one or more kinds of theabove-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.Further, the materials mentioned as the substrate material can also beused.

The plurality of pyramidal projections and films can be formed byforming a thin film by a sputtering method, a vacuum evaporation method,a PVD (physical vapor deposition) method, or a CVD (chemical vapordeposition) method such as a low-pressure CVD (LPCVD) method or a plasmaCVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, a brush coating method, aspray method, a flow coating method, or the like can be employed. Stillalternatively, an imprinting technique or a nanoimprinting techniquewith which a nanoscale three-dimensional structure can be formed by atransfer technology can be employed. Imprinting and nanoimprinting aretechniques with which a minute three-dimensional structure can be formedwithout using a photolithography process.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection over a surfaceand a high antireflection function that can further reduce light fromexternal by covering each pyramidal projection with a film having ahigher refractive index than the pyramidal projections. Accordingly, adisplay device with further high image quality and a high performancecan be provided.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 4

This embodiment mode describes an example of a display device having anantireflection function that can further reduce reflection of light fromexternal, for the purpose of providing excellent visibility.Specifically, this embodiment mode describes a liquid crystal displaydevice using a liquid crystal display element as a display element.

FIG. 8A is a top view of a liquid crystal display device having aplurality of pyramidal projections, and FIG. 8B is a cross-sectionalview of FIG. 8A along a line C-D. In the top view of FIG. 8A, theplurality of pyramidal projections are omitted.

As shown in FIG. 8A, a pixel region 606, a driver circuit region 608 athat is a scan line driver circuit region, and a driver circuit region608 b that is a scan line driver circuit region are sealed between asubstrate 600 and an opposite substrate 695 with a sealant 692. A drivercircuit region 607 that is a signal-line driver circuit region formedusing a driver IC is provided over a substrate 600. In the pixel region606, a transistor 622 and a capacitor 623 are provided, and in thedriver circuit region 608 b, a driver circuit including a transistor 620and a transistor 621 is provided. Note that reference numeral 602denotes an external terminal connection region, and 603 denotes a wiringregion. An insulating substrate similar to that in the above embodimentmode can be used as the substrate 600. Although there is concern that asubstrate made of a synthetic resin generally has lower allowabletemperature limit than other substrates, the substrate can be employedby transfer after a manufacturing process using a high heat-resistancesubstrate.

In the pixel region 606, the transistor 622 functioning as a switchingelement is provided over the substrate 600 with a base film 604 a and abase film 604 b interposed therebetween. In this embodiment mode, thetransistor 622 is a multi-gate thin film transistor (TFT), whichincludes a semiconductor layer including impurity regions that functionas a source region and a drain region, a gate insulating layer, a gateelectrode layer having a stacked structure of two layers, and a sourceelectrode layer and a drain electrode layer. The source electrode layeror the drain electrode layer is in contact with and electricallyconnects the impurity region of the semiconductor layer and a pixelelectrode layer 630. A thin film transistor can be manufactured by manymethods. For example, a crystalline semiconductor film is employed as anactive layer. A gate electrode is provided over a crystallinesemiconductor film with a gate insulating film interposed therebetween.An impurity element can be added to the active layer using the gateelectrode. By addition of an impurity element using the gate electrodein this manner, a mask does not need to be formed for addition of animpurity element. The gate electrode can have a single-layer structureor a stacked structure. The impurity region can be formed into ahigh-concentration impurity region and a low-concentration impurityregion by controlling the concentration thereof. A thin film transistorhaving a low-concentration impurity region in this manner is referred toas an LDD (Lightly Doped Drain) structure. The low-concentrationimpurity region can be formed to be overlapped by the gate electrode,and such a thin film transistor is referred to as a GOLD (GateOverlapped LDD) structure. The thin film transistor is formed to have ann-type polarity by using phosphorus (P) or the like in the impurityregion. In a case of a p-type polarity, boron (B) or the like may beadded. After that, an insulating film 611 and an insulating film 612 areformed to cover the gate electrode and the like. Dangling bonds of thecrystalline semiconductor film can be terminated by a hydrogen elementmixed in the insulating film 611 (and the insulating film 612).

In order to further improve planarity, an insulating film 615 and aninsulating film 616 may be formed as interlayer insulating films. Theinsulating film 615 and the insulating film 616 can be formed using anorganic material, an inorganic material, or a stacked structure thereof.For example, the insulating film 615 and the insulating film 616 can beformed of a material selected from substances including an inorganicinsulating material such as silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide, aluminum nitride, aluminumoxynitride, aluminum nitride oxide having a higher content of nitrogenthan that of oxygen, aluminum oxide, diamond-like carbon (DLC),polysilazane, a nitrogen-containing carbon (CN), PSG (phosphosilicateglass), BPSG (borophosphosilicate glass), and alumina. Alternatively, anorganic insulating material may be used; an organic material may beeither photosensitive or non-photosensitive; and polyimide, acrylic,polyamide, polyimide amide, a resist, benzocyclobutene, a sitoxaneresin, or the like can be used. Note that the siloxane resin correspondsto a resin having Si—O—Si bonds. Siloxane has a skeleton structureformed from a bond of silicon (Si) and oxygen (O). As a substituent, anorganic group containing at least hydrogen (for example, an alkyl groupor aromatic hydrocarbon) is used. A fluoro group may be used as thesubstituent. Alternatively, an organic group containing at leasthydrogen and a fluoro group may be used as the substituent.

By using a crystalline semiconductor film, the pixel region and thedriver circuit region can be formed over the same substrate. In thatcase, the transistor in the pixel region and the transistor in thedriver circuit region 608 b are formed simultaneously. The transistorused in the driver circuit region 608 b constitutes a part of a CMOScircuit. Although the thin film transistor included in the CMOS circuithas a GOLD structure, it may have an LDD structure like the transistor622.

Without limitation to this embodiment mode, the thin film transistor ofthe pixel region may have a single-gate structure in which a singlechannel formation region is formed, a double-gate structure in which twochannel formation regions are formed, or a triple-gate structure inwhich three channel formation regions are formed. In addition, the thinfilm transistor of a peripheral driver circuit region may also have asingle-gate structure, a double-gate structure, or a triple-gatestructure.

Note that without limitation to the manufacturing method of a thin filmtransistor described in this embodiment mode, the present invention canbe used in a top-gate structure (such as a staggered structure), abottom-gate structure (such as an inverted staggered structure), adual-gate structure including two gate electrode layers provided aboveand below a channel region each with a gate insulating film interposedtherebetween, or another structure.

Next, an insulating layer 631 called an orientation film is formed by aprinting method or a droplet discharge method to cover the pixelelectrode layer 630 and the insulating film 616. Note that theinsulating layer 631 can be selectively formed by using a screenprinting method or an offset printing method. After that, rubbingtreatment is performed. The rubbing treatment is not necessarilyperformed when the mode of liquid crystal is, for example, a VA mode. Aninsulating layer 633 functioning as an orientation film is similar tothe insulating layer 631. Then, the sealant 692 is formed by a dropletdischarge method in a peripheral region of the pixel region.

After that, the opposite substrate 695 provided with the insulatinglayer 633 functioning as an orientation film, a conductive layer 634functioning as an opposite electrode, a colored layer 635 functioning asa color filter, a polarizer 641 (also referred to as a polarizingplate), and pyramidal projections 642 each covered with a film 643 isattached to the substrate 600 that is a TFT substrate with a spacer 637interposed therebetween, and a liquid crystal layer 632 is provided in agap therebetween. Since the liquid crystal display device of thisembodiment mode is of transmissive type, a polarizer (polarizing plate)644 is provided on a side of the substrate 600 opposite to the side ofhaving elements. The polarizer can be provided over the substrate usingan adhesive layer. The sealant may be mixed with a filler, and further,the opposite substrate 695 may be provided with a shielding film (blackmatrix), or the like, Note that the color filter or the like may beformed of materials exhibiting red (R), green (G), and blue (B) when theliquid crystal display device performs full color display. Whenperforming monochrome display, the colored layer may be omitted orformed of a material exhibiting at least one color.

The display device in FIGS. 8A and 8B is an example in which thepyramidal projections 642 are provided on an outer side of the oppositesubstrate 695 and the polarizer 641, the colored layer 635, and theconductive layer 634 are sequentially provided on an inner side.However, the polarizer may be provided on the outer side of thesubstrate 695 (to a viewer side), and in that case, the pyramidalprojections with an antireflection function may be provided over asurface of the polarizer (polarizing plate). The stacked structure ofthe polarizer and the colored layer is also not limited to FIGS. 8A and8B and may be appropriately determined depending on materials of thepolarizer and the colored layer or conditions of a manufacturingprocess.

Note that the color filter is not provided in some cases wherelight-emitting diodes (LEDs) of RGB or the like are arranged as abacklight and a successive additive color mixing method (fieldsequential method) in which color display is performed by time divisionis employed. The black matrix is preferably provided so as to overlap atransistor and a CMOS circuit for the sake of reducing reflection oflight from external by wirings of the transistor and the CMOS circuit.Note that the black matrix may be provided so as to overlap a capacitor.This is because reflection by a metal film forming the capacitor can beprevented.

The liquid crystal layer can be formed by a dispenser method (droppingmethod), or an injecting method by which liquid crystal is injectedusing a capillary phenomenon after attaching the substrate 600 includingan element to the opposite substrate 695. A dropping method ispreferably employed when using a large-sized substrate to which it isdifficult to apply an injecting method.

Although the spacer may be provided in such a way that particles eachhaving a size of several micrometers are sprayed, the spacer in thisembodiment mode is formed by a method in which a resin film is formedover an entire surface of the substrate and then etched. A material ofthe spacer is applied by a spinner and then subjected to light exposureand development to form a predetermined pattern. Moreover, the materialis heated at 150° C. to 200° C. in a clean oven or the like so as to behardened. The thus manufactured spacer can have various shapes dependingon the conditions of the light exposure and development. It ispreferable that the spacer have a columnar shape with a flat top so thatmechanical strength of the liquid crystal display device can be securedwhen the opposite substrate is attached. The shape of the spacer can beconical, pyramidal, or the like, and there is no particular limitationon the shape.

Subsequently, a terminal electrode layer 678 electrically connected tothe pixel region is provided with an FPC 694 that is a wiring board forconnection, through an anisotropic conductive layer 696. The FPC 694functions to transmit signals or potential from external. Through theabove steps, a liquid crystal display device having a display functioncan be manufactured.

A wiring and a gate electrode layer which are included in thetransistor, the pixel electrode layer 630, and the conductive layer 634that is an opposite electrode layer can be formed using a materialselected from indium tin oxide (ITO), indium zinc oxide (IZO) in whichindium oxide is mixed with zinc oxide (ZnO), a conductive material inwhich indium oxide is mixed with silicon oxide (SiO₂), organoindium,organotin, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide, orindium tin oxide containing titanium oxide; a metal such as tungsten(W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V),niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni),titanium (i), platinum (Pt), aluminum (Al), copper (Cu) or silver (Ag),an alloy thereof, or metal nitride thereof.

The polarizing plate and the liquid crystal layer may be stacked with aretardation plate interposed therebetween.

In this embodiment mode, a plurality of pyramidal projections that areadjacent to each other are provided, and a refractive index of theprojection is made to change by a physical pyramidal shape from asurface of a display screen side to the outer side (air side), so thatreflection of light is prevented. In this embodiment mode, as shown inFIGS. 8A and 8B, the pyramidal projections 642 are provided over thesurface of the opposite substrate 695 to a viewer side of the displayscreen. In addition, the plurality of pyramidal projections 642 are eachcovered with the film 643 formed of a material with a higher refractiveindex than that of the pyramidal projection 642.

The display device of this embodiment mode includes a plurality ofpyramidal projections formed over its surface. Light from external isreflected not to a viewer side but to an adjacent pyramidal projectionbecause the surface of each projection is not flat with respect to thedisplay screen. Incident light from external is partly transmittedthrough each pyramidal projection, whereas reflected light is incidenton an adjacent pyramidal projection. In this manner, light reflected ata surface of the pyramidal projections repeats incidence betweenadjacent pyramidal projections.

In other words, the number of times of incidence on the pyramidalprojections among light from external is increased; therefore, theamount of light transmitted through the pyramidal projections isincreased. Thus, the amount of light from external which is reflected toa viewer side is reduced, and the cause of a reduction in visibilitysuch as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oftight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented. Since reflection ofincident light from external to the viewer side caused by the flatportions can be reduced, the degree of freedom for selection of shape,setting for arrangement, and a manufacturing process of the pyramidalprojections can be increased.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

In the present invention, in the case where the film and the pyramidalprojection have a large difference in reflactive index, it is preferablethat the thickness of the film be thin.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved. Even in a case of a structurein which flat portions are provided between the pyramidal projectionslike a conical shape, light incident on the flat portions is reduced dueto the light confinement effect inside the pyramidal projection by thefilm, and reflection to the viewer side can be further prevented.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced, and reliability isimproved. When conductivity is imparted by selecting a material of thefilm, other effective functions such as a function of prevention ofstatic electricity can be imparted. As a material that can be used forthe film, conductive titanium oxide having a high light-transmittingproperty in visible light; silicon nitride, silicon oxide, or aluminumoxide having high physical strength; aluminum nitride having high heatconductivity; or the like can be used.

In accordance with the present invention, an antireflection film(substrate) that has a plurality of pyramidal projections adjacent toeach other and a display device that has the antireflection film(substrate) can be provided, and a high antireflection function can begiven.

An antireflection film of the present invention is acceptable as long asthe film has a pyramidal projection covered with a film. The pyramidalprojection may be directly formed to have a single continuous structureover a surface of a film (substrate). For example, the surface of thefilm (substrate) is processed, and the pyramidal projection may beformed thereover, or the film (substrate) may be selectively formed tohave a pyramidal projection by a printing method such as nanoimprinting.Alternatively, the pyramidal projection may be formed over the film(substrate) in another step.

The plurality of pyramidal projections may be a single continuous filmor be independently arranged over the substrate.

For the film, a material with a higher refractive index than at least amaterial used for the pyramidal projection may be used. Accordingly, amaterial used for the film is determined relative to a material of asubstrate for partly constituting a display screen of a display deviceand a material of the pyramidal projection formed over the substrate.Therefore, the material used for the film can be determined asappropriate.

A material used for forming the pyramidal projection and the film may beappropriately selected in accordance with a material of the substratepartly forming a display screen surface, such as silicon, nitrogen,fluorine, oxide, nitride, or fluoride. The oxide may be silicon oxide(SiO₂), boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO),aluminum oxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide(CaO), diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide(SrO), antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide(ITO), zinc oxide (ZnO), indium zinc oxide (IZO) in which indium oxideis mixed with zinc oxide (ZnO), a conductive material in which indiumoxide is mixed with silicon oxide (SiO₂), organic indium, organic tin,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. The nitride may be aluminumnitride (AlN), silicon nitride (Si), or the like. The fluoride may belithium fluoride (LiF), sodium fluoride (NaF), magnesium fluoride(MgF₂), calcium fluoride (CaF₂), lanthanum fluoride (LaF₃), or the like.The pyramidal projection and the film may include one or more kinds ofthe above-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.Further, the materials mentioned as the substrate material can also beused.

The plurality of pyramidal projections and films can be formed byforming a thin film by a sputtering method, a vacuum evaporation method,a PVD (physical vapor deposition) method, or a CVD (chemical vapordeposition) method such as a low-pressure CVD (LPCVD) method or a plasmaCVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, a brush coating method, aspray method, a flow coating method, or the like can be employed. Stillalternatively, an imprinting technique or a nanoimprinting techniquewith which a nanoscale three-dimensional structure can be formed by atransfer technology can be employed. Imprinting and nanoimprinting aretechniques with which a minute three-dimensional structure can be formedwithout using a photolithography process.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 5

This embodiment mode describes an example of a display device having anantireflection function that can further reduce reflection of light fromexternal, for the purpose of providing excellent visibility.Specifically, this embodiment mode describes a light-emitting displaydevice using a light-emitting element as a display element. Amanufacturing method of the display device in this embodiment mode isdescribed in detail with reference to FIGS. 9A and 9B and FIG. 12.

Base films 101 a and 101 b are formed over a substrate 100 having aninsulating surface. In this embodiment mode, the base film 101 a isformed using a silicon nitride oxide film to have a thickness of 10 nmto 200 nm (preferably, 50 nm to 150 nm), and the base film 101 b isformed using a silicon oxynitride film to have a thickness of 50 to 200nm (preferably, 100 to 150 nm). The base film 101 a and the base film101 b are stacked as one base film. In this embodiment mode, the basefilm 101 a and the base film 101 b are formed using a plasma CVD method.

As a material of the base film, an acrylic acid, a methacrylic acid, ora derivative thereof a heat-resistant high molecular compound such aspolyimide, aromatic polyamide, or polybenzimidazole; or a siloxane resinmay be used. Alternatively, a resin material such as a vinyl resin likepolyvinyl alcohol or polyvinylbutyral, an epoxy resin, a phenol resin, anovolac resin, an acrylic resin, a melamine resin, of a urethane resinmay be used. Further, an organic material such as benzocyclobutene,parylene, fluorinated arylene ether, or polyimide, a compositionmaterial containing a water-soluble homopolymer and a water-solublecopolymer, or the like may be used. Moreover, an oxazole resin can beused, and for example, a photo-curing polybenzoxazole or the like can beused.

The base film can be formed by a sputtering method, a PVD method(physical vapor deposition), a CVD (chemical vapor deposition) methodsuch as a low-pressure CVD method (LPCVD method), or a plasma CVDmethod, or the like. Alternatively, a droplet discharge method, aprinting method (a method for forming a pattern such as screen printingor offset printing), a coating method such as a spin coating method, adipping method, a dispenser method, or the like can also be used.

As the substrate 100, a glass substrate, a quartz substrate, or the likecan be used. In addition, a plastic substrate having heat resistancesufficient to withstand a processing temperature of this embodiment modemay be used, or a flexible film-like substrate may be used. As theplastic substrate, a substrate made of PET (polyethylene terephthalate),PEN polyethylenenaphthalate), or PES (polyethersulfone) can be used, andas the flexible substrate, a substrate made of a synthetic resin such asacrylic can be used. Since the display device manufactured in thisembodiment mode has a structure in which light from a light-emittingelement is extracted through the substrate 100, the substrate 100 needsto have a light-transmitting property.

The base film can be formed using silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, or the like and may haveeither a single-layer structure or a stacked structure of two or morelayers.

Next, a semiconductor film is formed over the base film. Thesemiconductor film may be formed with a thickness of 25 nm to 200 nmpreferably, 30 nm to 150 nm) by any of various methods (such as asputtering method, an LPCVD method, or a plasma CVD method). In thisembodiment mode, it is preferable to use a crystalline semiconductorfilm which is obtained by crystallizing an amorphous semiconductor filmwith a laser beam.

The semiconductor film obtained in this manner may be doped with aslight amount of an impurity element (boron or phosphorus) to control athreshold voltage of a thin film transistor. This doping with animpurity element may be performed to the amorphous semiconductor filmbefore the crystallization step. When the doping with an impurityelement is performed to the amorphous semiconductor film, activation ofthe impurity element can be performed by subsequent heat treatment forcrystallization. In addition, defects and the like caused by doping canbe improved.

Next, the crystalline semiconductor film is etched into a desired shapeto form a semiconductor layer.

The etching may be performed by either plasma etching (dry etching) orwet etching; however, plasma etching is suitable for treating alarge-sized substrate. As an etching gas, a fluorine-based gas such asCF₄ or NF₃ or a chlorine-based gas such as Cl₂ or BCl₃ is used, to whichan inert gas such as He or Ar may be appropriately added. Alternatively,electric discharge machining can be performed locally when the etchingis performed using atmospheric pressure discharge, in which case a masklayer does not need to be formed over the entire surface of thesubstrate.

In the present invention, a conductive layer forming a wiring layer oran electrode layer, a mask layer used for forming a predeterminedpattern, or the like may be formed by a method capable of selectivelyforming a pattern, such as a droplet discharge method. A dropletdischarge (ejection) method (also referred to as an ink-jet methoddepending on its method) can form a predetermined pattern (of aconductive layer or an insulating layer) by selectively discharging(ejecting) droplets of a composition mixed for a specific purpose. Inthis case, treatment for controlling wettability or adhesiveness may beperformed to a subject region. Alternatively, a method by which apattern can be transferred or drawn, such as a printing method (a methodfor forming a pattern such as screen printing or offset printing), adispenser method, a brush coating method, a spray method, a flow coatingmethod, or the like can be used.

A mask used in this embodiment mode is formed using a resin materialsuch as an epoxy resin, an acrylic resin, a phenol resin, a novolacresin, a melamine resin, or a urethane resin. Alternatively, an organicmaterial such as benzocyclobutene, parylene, fluorinated arylene ether,or polyimide having a light-transmitting property; a compound materialmade by polymerization of a siloxane-based polymer or the like; acomposition material containing a water-soluble homopolymer and awater-soluble copolymer; or the like may be used. Still alternatively, acommercial resist material containing a photosensitizer may be used. Forexample, a positive resist, a negative resist, or the like may be used.In a case of using a droplet discharge method, even when using any ofthe above materials, a surface tension and a viscosity are appropriatelycontrolled by adjusting the concentration of a solvent or adding asurfactant or the like.

A gate insulating layer 107 is formed to cover the semiconductor layer.The gate insulating layer is formed using an insulating film containingsilicon with a thickness of 10 nm to 150 nm by a plasma CVD method, asputtering method, or the like. The gate insulating layer may be formedusing a known material such as an oxide material or nitride material ofsilicon typified by silicon nitride, silicon oxide, silicon oxynitride,or silicon nitride oxide, and it may have either a single-layerstructure or a JO stacked structure. The gate insulating layer may beformed to have a three-layer structure of a silicon nitride film, asilicon oxide film, and a silicon nitride film. Alternatively, a singlelayer of a silicon oxynitride film or a stacked layer of two layers maybe used.

Next, a gate electrode layer is formed over the gate insulating layer107. The gate electrode layer can be formed by a sputtering method, anevaporation method, a CVD method, or the like. The gate electrode layermay be formed using an element selected from tantalum (Ta), tungsten(W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper, (Cu),chromium (Cr), and neodymium (Nd), or an alloy material or a compoundmaterial containing the above element as its main component.Alternatively, the gate electrode layer may be formed using asemiconductor film typified by a polycrystalline silicon film doped withan impurity element such as phosphorus, or an AgPdCu alloy. The gateelectrode layer may be a single layer or stacked layers.

Although the gate electrode layer is formed in a tapered shape in thisembodiment mode, the present invention is not limited thereto. The gateelectrode layer may have a stacked structure in which only one layer hasa tapered shape and the other layer has a perpendicular side surface byanisotropic etching. The gate electrode layers stacked may havedifferent taper angles or the same taper angle, as in this embodimentmode. When the gate electrode layer has a tapered shape, the coveragethereof by a film to be stacked thereover is improved, and defects canbe reduced. Accordingly, reliability is improved.

Through the etching step in forming the gate electrode layer, the gateinsulating layer 107 may be etched to a certain extent and the thicknessthereof may be reduced (so-called film reduction).

An impurity element is added to the semiconductor layer to form animpurity region. The impurity region can be formed into ahigh-concentration impurity region and a low-concentration impurityregion by controlling the concentration thereof. A thin film transistorhaving a low-concentration impurity region is referred to as an LDD(Lightly Doped Drain) structure. The low-concentration impurity regioncan be formed to be overlapped by the gate electrode and such a thinfilm transistor is referred to as a GOLD (Gate Overlapped LDD)structure. The thin film transistor is formed to have an n-type polarityby using phosphorus (P) in the impurity region. In a case of a p-typepolarity, boron (B) or the like may be added.

In this embodiment mode, a region where the impurity region isoverlapped by the gate electrode layer with the gate insulating layerinterposed therebetween is referred to as a Lov region, and a regionwhere the impurity region is not overlapped by the gate electrode layerwith the gate insulating layer interposed therebetween is referred to asa Loff region. In FIG. 9B, the impurity regions are indicated byhatching and white, which does not mean that an impurity element is notadded to the white portion. They are indicated in this manner so that itis easily recognized that the concentration distribution of an impurityelement in this region reflects a mask or conditions of doping. Notethat this applies to other drawings of this specification.

Heat treatment, intense light irradiation, or laser light irradiationmay be performed to activate the impurity element. At the same time asthe activation, plasma damage to the gate insulating layer and theinterface between the gate insulating layer and the semiconductor layercan be repaired.

Then, a first interlayer insulating layer is formed to cover the gateelectrode layer and the gate insulating layer. In this embodiment mode,the first interlayer insulating layer has a stacked structure of aninsulating film 167 and an insulating film 168. The insulating film 167and the insulting film 168 can be formed using a silicon nitride film, asilicon nitride oxide film, a silicon oxynitride film, a silicon oxidefilm, or the like by a sputtering method or a plasma CVD method, oranother insulating film containing silicon may be used as a single layeror a stacked structure of three or more layers.

In addition, heat treatment is performed in a nitrogen atmosphere at300° C. to 550° C. for 1 to 12 hours to hydrogenate the semiconductorlayer. Preferably, it is performed at 400° C. to 500° C. This step is astep of terminating dangling bonds of the semiconductor layer withhydrogen which is contained in the insulating film 167 that is theinterlayer insulating layer. In this embodiment mode, heat treatment isperformed at 410° C.

The insulating film 167 and the insulating film 168 can be formed usinga material selected from substances including an inorganic insulatingmaterial, such as aluminum nitride (AlN), aluminum oxynitride (AlON),aluminum nitride oxide (AlNO) having a higher content of nitrogen thanthat of oxygen, aluminum oxide, diamond-like carbon (DLC),nitrogen-containing carbon (CN), and polysilazane. Alternatively, amaterial containing siloxane may be used. An organic insulating materialmay be used, and as an organic material, polyimide, acrylic, polyamide,polyimide amide, a resist, or benzocyclobutene can be used. Moreover, anoxazole resin can be used, and for example, a photo-curingpolybenzoxazole or the like can be used.

Next, a contact hole (opening) is formed in the insulating film 167, theinsulating film 168, and the gate insulating layer 107 using a mask madeof a resist so as to reach the semiconductor layer. A conductive film isformed to cover the opening, and the conductive film is etched to form asource electrode layer or a drain electrode layer which is electricallyconnected to a part of a source region or a drain region. The sourceelectrode layer or drain electrode layer can be formed by forming aconductive film by a PVD method, a CVD method, an evaporation method, orthe like and then etching the conductive film into a desired shape. Aconductive layer can be selectively formed in a predetermined positionby a droplet discharge method, a printing method, a dispenser method, anelectroplating method, or the like. Furthermore, a reflow method or adamascene method may be used. The source electrode layer or drainelectrode layer is formed using a material such as Ag, Au, Cu, Ni, Pt,Pd, Ir, Rh, w Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, Si, or Ge, or an alloyor a metal nitride thereof. In addition, it may have a stacked structurethereof.

Through the above steps, an active matrix substrate can be manufactured,which includes a thin film transistor 285 that is a p-channel thin filmtransistor having a p-type impurity region in a tov region and a thinfilm transistor 275 that is an n-channel thin film transistor having ann-type impurity region in a Lov region in a peripheral driver circuitregion 204, and a thin film transistor 265 that is a multi-channeln-channel thin film transistor having an n-type impurity region in aLoff region and a thin film transistor 245 that is a p-channel thin filmtransistor having a p-type impurity region in a Lov region in the pixelregion 206.

Without limitation to this embodiment mode, a thin film transistor mayhave a single-gate structure in which a single channel formation regionis formed, a double-gate structure in which two channel formationregions are formed, or a triple-gate structure in which three channelformation regions are formed. In addition, the thin film transistor inthe peripheral driver circuit region may also have a single-gatestructure, a double-gate structure, or a triple-gate structure.

Next, an insulating film 181 is formed as a second interlayer insulatinglayer. In FIGS. 9A and 9B, a reference numeral 201 denotes a separationregion for separation by scribing; 202, an external terminal connectionregion which is an attachment portion of an FPC; 203, a wiring regionwhich is a lead wiring region of a peripheral portion; 204, a peripheraldriver circuit region; and 206, a pixel region. In the wiring region203, a wiring 179 a and a wiring 179 b are provided, and in the externalterminal connection region 202, a terminal electrode layer 178 connectedto an external terminal is provided.

The insulating film 181 can be formed of a material selected fromsubstances including an inorganic insulating material such as siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide,aluminum nitride (AlN), aluminum oxide containing nitrogen (alsoreferred to as aluminum oxynitride) (AlON), aluminum nitride containingoxygen (also referred to as aluminum nitride oxide) (AlNO), aluminumoxide, diamond-like carbon (DLC), nitrogen-containing carbon (CN), PSG(phosphosilicate glass), BPSG (borophosphosilicate glass), and alumina.Alternatively, a siloxane resin may be used. Furthermore, an organicinsulating material may be used; an organic insulating material may beeither photosensitive or non-photosensitive; and polyimide, acrylic,polyamide, polyimide amide, a resist, benzocyclobutene, polysilazane, ora low-dielectric constant material can be used. Moreover, an oxazoleresin can be used, and for example, a photo-curing polybenzoxazole orthe like can be used. Since an interlayer insulating layer provided forplanarization needs to have high heat resistance, high insulatingproperty, and high planarity, the insulating film 181 is preferablyformed by a coating method typified by a spin coating method.

Instead, the insulating film 181 can be formed by dipping, spraycoating, a doctor knife, a roll coater, a curtain coater, a knifecoater, CVD, evaporation, or the like. The insulating film 181 may beformed by a droplet discharge method. In a case of using a dropletdischarge method, a material liquid can be saved. Alternatively, amethod like a droplet discharge method by which a pattern can betransferred or drawn, such as a printing method (a method for forming apattern such as screen printing or offset printing), a dispenser method,a brush coating method, a spray method, a flow coating method, or thelike can be used.

A minute opening, that is, a contact hole is formed in the insulatingfilm 181 in the pixel region 206.

Next, a first electrode layer 185 (also referred to as a pixel electrodelayer) is formed in contact with the source electrode layer or the drainelectrode layer. The first electrode layer 185 functions as an anode ora cathode, and may be formed using a film containing the followingmaterial as its main component: an element selected from Ti, Ni, W, Cr,Pt, Zn, Sn, In, and Mo; or an alloy or compound material containing theabove element such as titanium nitride, TiSi_(X)N_(Y), WSi_(X), tungstennitride, WSi_(X)N_(Y), or NbN, or a stacked film thereof with a totalthickness of 100 nm to 800 nm.

In this embodiment mode, the display device has a structure in which alight-emitting element is used as a display element and light from thelight-emitting element is extracted through the first electrode layer185; therefore, the first electrode layer 185 has a light-transmittingproperty. The first electrode layer 185 is formed by forming atransparent conductive film and then etching the transparent conductivefilm into a desired shape.

In the present invention, the first electrode layer 185 that is alight-transmitting electrode layer may be specifically formed using atransparent conductive film made of a conductive material having alight-transmitting property, such as indium oxide containing tungstenoxide, indium zinc oxide containing tungsten oxide, indium oxidecontaining titanium oxide, or indium tin oxide containing titaniumoxide. It is needless to say that indium tin oxide (ITO), indium zincoxide (IZO), indium tin oxide to which silicon oxide is added (ITSO), orthe like can also be used.

Even in a case of using a material such as a metal film which does nothave a light-transmitting property, light can be transmitted through thefirst electrode layer 185 by forming the first electrode layer 185 verythin (preferably, a thickness of approximately 5 nm to 30 nm) so as tobe able to transmit light. A metal thin film which can be used for thefirst electrode layer 185 is a conductive film made of titanium,tungsten, nickel, gold, platinum, silver, aluminum, magnesium, calcium,lithium, or an alloy thereof.

The first electrode layer 185 can be formed by an evaporation method, asputtering method, a CVD method, a printing method, a dispenser method,a droplet discharge method, or the like. In this embodiment mode, thefirst electrode layer 185 is manufactured by a sputtering method usingindium zinc oxide containing tungsten oxide. The first electrode layer185 preferably has a thickness in total of 100 nm to 800 nm.

The first electrode layer 185 may be polished by a CMP method or bycleaning with a polyvinyl alcohol-based porous body so that a surface ofthe first electrode layer 185 is planarized. After polishing by a CMPmethod, ultraviolet irradiation, oxygen plasma treatment, or the likemay be performed to the surface of the first electrode layer 185.

After the first electrode layer 185 is formed, heat treatment may beperformed. Through this heat treatment, moisture included in the firstelectrode layer 185 is released. Therefore, degasification or the likeis not caused in the first electrode layer 185. Even when alight-emitting material which is easily deteriorated by moisture isformed over the first electrode layer, the light-emitting material isnot deteriorated. Accordingly, a highly reliable display device can bemanufactured.

Next, an insulating layer 186 (also called a partition, a barrier, orthe like) is formed to cover an end portion of the first electrode layer185, and the source electrode layer or the drain electrode layer.

The insulating layer 186 can be formed using silicon oxide, siliconnitride, silicon oxynitride, silicon nitride oxide, or the like and mayhave a single-layer structure or a stacked structure of two layers,three layers, or the like. The insulating layer 186 can alternatively beformed using a material selected from substances including an inorganicinsulating material, such as aluminum nitride, aluminum oxynitridehaving a higher content of oxygen than that of nitrogen, aluminumnitride oxide having a higher content of nitrogen than that of oxygen,aluminum oxide, diamond-like carbon (DLC), nitrogen-containing carbon,or polysilazane. Alternatively, a material containing siloxane may beused. Furthermore, an organic insulating material may be used; anorganic insulating material may be either photosensitive ornon-photosensitive; and polyimide, acrylic, polyamide, polyimide amide,a resist, benzocyclobutene, or polysilazane can be used. Moreover, anoxazole resin can be used, and for example, a photo-curingpolybenzoxazole or the like can be used.

The insulating layer 186 can be formed by a sputtering method, a PVD(physical vapor deposition) method, a CVD (chemical vapor deposition)method such as a low-pressure CVD (LPCVD) method or a plasma CVD method,a droplet discharge method by which a pattern can be formed selectively,a printing method by which a pattern can be transferred or drawn (amethod for forming a pattern such as screen printing or offsetprinting), a dispenser method, a coating method such as a spin coatingmethod, a dipping method, or the like.

The etching into a desired shape may be performed by either plasmaetching (dry etching) or wet etching; however, plasma etching issuitable for treating a large-sized substrate. As an etching gas, afluorine-based gas such as CF₄ or NF₃ or a chlorine-based gas such asCl₂ or BCl₃ is used, to which an inert gas such as He or Ar may beappropriately added. Alternatively, electric discharge machining may beperformed locally when the etching process is performed usingatmospheric pressure discharge, in which case a mask layer does not needto be formed over the entire surface of the substrate.

In the connection region 205 shown in FIG. 9A, a wiring layer formed ofthe same material and in the same step as the second electrode layer iselectrically connected to the wiring layer which is formed of the samematerial and in the same step as the gate electrode layer.

A light-emitting layer 188 is formed over the first electrode layer 185.Note that, although FIG. 9B shows only one pixel, respectiveelectroluminescent layers corresponding to colors of R (red), G (green),and B (blue) are separately formed in this embodiment mode.

Next, a second electrode layer 189 is formed using a conductive filmover the light-emitting layer 188. For the second electrode layer 189,Al, Ag, Li, Ca, an alloy or a compound thereof such as MgAg, MgIn, AlLi,or CaF₂, or calcium nitride may be used. Thus, a light-emitting element190 including the first electrode layer 185, the light-emitting layer188, and the second electrode layer 189 is formed (see FIG. 911).

In the display device of this embodiment mode shown in FIGS. 9A and 9B,light emitted from the light-emitting element 190 is transmitted throughthe first electrode layer 185 and extracted in a direction indicated byan arrow in FIG. 9B.

In this embodiment mode, an insulating layer may be provided as apassivation film protective film) over the second electrode layer 189.It is effective to provide a passivation film to cover the secondelectrode layer 189 in this manner. The passivation film can be formedusing a single layer or a stacked layer of an insulating film includingsilicon nitride, silicon oxide, silicon oxynitride, silicon nitrideoxide, aluminum nitride, aluminum oxynitride, aluminum nitride oxidehaving a higher content of nitrogen than that of oxygen, aluminum oxide,diamond-like carbon (DLC), or nitrogen-containing carbon. Alternatively,the passivation film may be formed using a siloxane resin.

In this case, a film providing good coverage is preferably used as thepassivation film. A carbon film, especially, a DLC film is effective.The DLC film can be formed at a temperature in the range of roomtemperature to 100° C.; therefore, the DLC film can be easily formedover the light-emitting layer 188 having low heat resistance. The DLCfilm can be formed by a plasma CVD method (typically, an RF plasma CVDmethod, a microwave CVD method, an electron cyclotron resonance (ECR)CVD method, a thermal filament CVD method, or the like), a combustionflame method, a sputtering method, an ion-beam evaporation method, alaser evaporation method, or the like. A hydrogen gas and ahydrocarbon-based gas (for example, CH₄, C₂H₂, C₆H₆, or the like) areused as a reaction gas which is used for forming a DLC film. Thereaction gas is ionized by glow discharge, and the ions are acceleratedto collide with a negatively self-biased cathode; accordingly, a DLCfilm is formed. A CN film may be formed using a C₂H₄ gas and an N₂ gasas a reaction gas. The DLC film has a high blocking effect on oxygen andcan suppress oxidation of the light-emitting layer 188. Accordingly, thelight-emitting layer 188 can be prevented from oxidizing during asubsequent sealing step.

The substrate 100 provided with the lightemitting element 190 and asealing substrate 195 are fixed to each other with a sealant 192 to sealthe light-emitting element (see FIGS. 9A and 9B). As the sealant 192, itis typically preferable to use a visible light curable resin, anultraviolet ray curable resin, or a heat curable resin. For example, abisphenol-A liquid resin, a bisphenol-A solid resin, abromine-containing epoxy resin, a bisphenol-F resin, a bisphenol-ADresin, a phenol resin, a cresol resin, a novolac resin, a cycloaliphaticepoxy resin, an Epi-Bis type (Epichlorohydrin-Bisphenol) epoxy resin, aglycidyl ester resin, a glycidyl amine resin, a heterocyclic epoxyresin, or a modified epoxy resin can be used. Note that a regionsurrounded by the sealant may be filled with a filler 193, or nitrogenmay be enclosed by sealing the region in a nitrogen atmosphere. Sincethe display device of this embodiment mode is of bottom emission type,the filler 193 does not need to have a light-transmitting property.However, in a case of employing a structure in which light is extractedthrough the filler 193, the filler 193 needs to have alight-transmitting property. Typically, a visible light curing,ultraviolet curing, or thermosetting epoxy resin may be used. Throughthe above steps, a display device having a display function with the useof a light-emitting element of this embodiment mode is completed.Alternatively, the filler can be dropped in a liquid state andencapsulated in the display device. When a substance having ahygroscopic property such as a drying agent is used as the filler, ahigher water-absorbing effect can be obtained, and element deteriorationcan be prevented.

In order to prevent element deterioration due to moisture, a dryingagent is provided in an EL display panel. In this embodiment mode, thedrying agent is provided in a depression portion formed in the sealingsubstrate so as to surround the pixel region, so that it does notinterfere with a reduction in thickness. Further, since awater-absorbing region is formed in a large area by forming the dryingagent in a region corresponding to the gate wiring layer, a highwater-absorbing effect can be obtained. In addition, since the dryingagent is also formed over the gate wiring layer which does not emitlight as itself, a reduction in light extraction efficiency can beprevented.

This embodiment mode describes the case where the light-emitting elementis sealed with a glass substrate. Sealing treatment is treatment forprotecting the light-emitting element from moisture. Therefore, any ofthe following method can be used: a method in which a light-emittingelement is mechanically sealed with a cover material, a method in whicha light emitting element is sealed with a thermosetting resin or anultraviolet curable resin, and a method in which a light-emittingelement is sealed with a thin film of metal oxide, metal nitride, or thelike having high barrier capability. As the cover material, glass,ceramics, plastic, or a metal can be used. However, when light isemitted to the cover material side, the cover material needs to have alight-transmitting property. The cover material is attached to thesubstrate over which the above-mentioned light-emitting element isformed, with a sealant such as a thermosetting resin or an ultravioletcurable resin, and a sealed space is formed by curing the resin withheat treatment or ultraviolet light irradiation treatment. It is alsoeffective to provide a moisture absorbing material typified by bariumoxide in the sealed space. The moisture absorbing material may beprovided on the sealant or over a partition or a peripheral portion soas not to block light emitted from the light-emitting element. Further,a space between the cover material and the substrate over which thelight-emitting element is formed can also be filled with a thermosettingresin or an ultraviolet curable resin. In this case, it is effective toadd a moisture absorbing material typified by barium oxide in thethermosetting resin or the ultraviolet curable resin.

FIG. 12 shows an example in which the source electrode or the drainelectrode layer is connected to the first electrode layer through awiring layer so as to be electrically connected instead of beingdirectly in contact, in the display device of FIGS. 9A and 9Bmanufactured in this embodiment mode. In the display device shown inFIG. 12, the source electrode layer or the drain electrode layer of thethin film transistor which drives the light-emitting element iselectrically connected to a first electrode layer 395 through a wiringlayer 199. Moreover, in FIG. 12, the first electrode layer 395 ispartially stacked over the wiring layer 199; however, the firstelectrode layer 395 may be formed first and then the wiring layer 199may be formed on the first electrode layer 395.

In this embodiment mode, an FPC 194 is connected to the terminalelectrode layer 178 by an anisotropic conductive layer 196 in theexternal terminal connection region 202 so as to have an electricalconnection with outside. Moreover, as shown in FIG. 9A that is a topview of the display device, the display device manufactured in thisembodiment mode includes a peripheral driver circuit region 207 and aperipheral driver circuit region 208 having scan line driver circuits,in addition to the peripheral driver circuit region 204 and a peripheraldriver circuit region 209 having signal line driver circuits.

In this embodiment mode, the above-described circuits are used; however,the present invention is not limited thereto and an IC chip may bemounted as a peripheral driver circuit by a COG method or a TAB method.Moreover, a gate-line driver circuit and a source-line driver circuitmay be provided in any number.

In the display device of the present invention, a driving method forimage display is not particularly limited, and for example, a dotsequential driving method, a line sequential driving method, an areasequential driving method, or the like may be used. Typically, the linesequential driving method is used, and a time division gray scaledriving method or an area gray scale driving method may be appropriatelyused. Further, a video signal inputted to the source line of the displaydevice may be either an analog signal or a digital signal. The drivercircuit and the like may be appropriately designed in accordance withthe video signal.

In this embodiment mode, a plurality of pyramidal projections that areadjacent to each other are provided, and a refractive index of theprojection is made to change by a physical pyramidal shape from asurface side of a display screen to the outer side (air side), so thatreflection of light is prevented. Since each of the display devicesshown in FIGS. 9A and 9B and FIG. 12 has a bottom-emission structure,light is emitted through the substrate 100. Therefore, a viewer side ison the substrate 100 side. A light-transmitting substrate is used as thesubstrate 100, and pyramidal projections 177 are provided on an outerside that corresponds to the viewer side. In addition, the plurality ofpyramidal projections 177 are each covered with a film 176 formed of amaterial with a higher refractive index than the pyramidal projections177.

The display device of this embodiment mode includes a plurality ofpyramidal projections formed over its surface. Light from external isreflected not to a viewer side but to an adjacent pyramidal projectionbecause the surface of each projection is not flat with respect to thedisplay screen. Incident light from external is partly transmittedthrough each pyramidal projection, whereas reflected light is thenincident on an adjacent pyramidal projection. In this manner, lightreflected at a surface of the pyramidal projections repeats incidencebetween adjacent pyramidal projections.

In other words, the number of times of incidence on the pyramidalprojections among light from external is increased; therefore, theamount of light transmitted through the pyramidal projections isincreased. Thus, the amount of light from external which is reflected toa viewer side is reduced, and the cause of a reduction in visibilitysuch as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented. Since reflection ofincident light from external to the viewer side caused by the flatportions can be reduced, the degree of freedom for selection of shape,setting for arrangement, and a manufacturing process of the pyramidalprojections can be increased.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

In the present invention, in the case where the film and the pyramidalprojection have a large difference in reflactive index, it is preferablethat the thickness of the film be thin.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved. Even in a case of a structurein which flat portions are peovided between the pyramidal projectionslike a conical shape, light incident on the flat portions is reduced dueto the light confinement effect inside the pyramidal projection by thefilm, and reflection to the viewer side can be further prevented.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced, and reliability isimproved. When conductivity is imparted by selecting a material of thefilm, other effective functions such as a function of prevention ofstatic electricity can be imparted. As a material that can be used forthe film, conductive titanium oxide having a high light-transmittingproperty in visible light; silicon nitride, silicon oxide, or aluminumoxide having high physical strength; aluminum nitride having high heatconductivity; or the like can be used.

In accordance with the present invention, an antireflection film(substrate) that has a plurality of pyramidal projection adjacent toeach other and a display device that has the antireflection film(substrate) can be provided, and a high antireflection function can begiven.

An antireflection film of the present invention is acceptable as long asthe film has a pyramidal projection covered with a film. The pyramidalprojection may be directly formed to have a single continuous structureover a surface of a film (substrate). For example, the surface of thefilm (substrate) is processed, and the pyramidal projection may beformed thereover, or the film (substrate) may be selectively formed tohave a pyramidal projection by a printing method such as nanoimprinting.Alternatively, the pyramidal projection may be formed over the film(substrate) in another step.

The plurality of pyramidal projections may be a single continuous filmor be independently arranged over the substrate.

As the film, a material with a higher refractive index than at least amaterial used for the pyramidal projection may be used. Accordingly, amaterial used for the film is determined relative to a material of asubstrate for partly constituting a display screen of a display deviceand a material of the pyramidal projection formed over the substrate.Therefore, the material used for the film can be determined asappropriate.

A material used for forming the pyramidal projection and the film may beappropriately selected in accordance with a material of the substratepartly forming a display screen surface, such as silicon, nitrogen,fluorine, oxide, nitride, or fluoride. The oxide may be silicon oxide(SiO₂), boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO),aluminum oxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide(CaO), diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide(SrO), antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide(ITO), zinc oxide (ZnO), indium zinc oxide (IZO) in which indium oxideis mixed with zinc oxide (ZnO), a conductive material in which indiumoxide is mixed with silicon oxide (SiO₂), organic indium, organic tin,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. The nitride may be aluminumnitride (AlN), silicon nitride (SiN), or the like. The fluoride may belithium fluoride (LiF), sodium fluoride (NaF), magnesium fluoride(MgF₂), calcium fluoride (CaF₂), lanthanum fluoride (LaF₃), or the like.The pyramidal projection and the film may include one or more kinds ofthe above-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.

The plurality of pyramidal projections and films can be formed byforming a thin film by a sputtering method, a vacuum evaporation method,a PVD (physical vapor deposition) method, or a CVD (chemical vapordeposition) method such as a low-pressure CVD (LPCVD) method or a plasmaCVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, or the like can beemployed. Still alternatively, an imprinting technique or ananoimprinting technique with which a nanoscale three-dimensionalstructure can be formed by a transfer technology can be employed.Imprinting and nanoimprinting are techniques with which a minutethree-dimensional structure can be formed without using aphotolithography process.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 6

A display device having a light-emitting element can be formed byapplying the present invention, and the element emits light by any oneof bottom emission, top emission, and dual emission. This embodimentmode describes examples of dual emission and top emission with referenceto FIGS. 10 and 11.

A display device shown in FIG. 11 includes an element substrate 1600, athin film transistor 1655, a thin film transistor 1665, a thin filmtransistor 1675, a thin film transistor 1685, a first electrode layer1617, a light-emitting layer 1619, a second electrode layer 1620, afiller 1622, a sealant 1632, an insulating film 1601 a, an insulatingfilm 1601 h, a gate insulating layer 1610, an insulating film 1611, aninsulating film 1612, an insulating layer 1614, a sealing substrate1625, a wiring layer 1633, a terminal electrode layer 1681, ananisotropic conductive layer 1682, an FPC 1683, pyramidal projections1627 a and 1627 b, and films 1628 a and 1628 b. The display device alsoincludes an external terminal connection region 232, a sealing region233, a peripheral driver circuit region 234, and a pixel region 236. Thefiller 1622 can be formed by a dropping method using a composition in aliquid state. A light-emitting display device is sealed by attaching theelement substrate 1600 provided with the filler by a dropping method andthe sealing substrate 1625 to each other.

The display device shown in FIG. 11 has a dual-emission structure, inwhich light is emitted through both the element substrate 1600 and thesealing substrate 1625 in directions of arrows. Therefore, alight-transmitting electrode layer is used as each of the firstelectrode layer 1617 and the second electrode layer 1620.

In this embodiment mode, the first electrode layer 1617 and the secondelectrode layer 1620 each of which is a light-transmitting electrodelayer may be formed using a transparent conductive film made of aconductive material having a light-transmitting property, specifically,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. It is needless to say thatindium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide towhich silicon oxide is added (ITSO), or the like can also be used.

Even in a case of using a material such as a metal film which does nothave a light-transmitting property, light can be transmitted through thefirst electrode layer 1617 and the second electrode layer 1620 byforming the first electrode layer 1617 and the second electrode layer1620 very thin (preferably, a thickness of approximately 5 nm to 30 nm)so as to be able to transmit light. A metal thin film which can be usedfor the first electrode layer 1617 and the second electrode layer 1620is a conductive film made of titanium, tungsten, nickel, gold, platinum,silver, aluminum, magnesium, calcium, lithium, or an alloy thereof.

As described above, the display device of FIG. 11 has a structure inwhich light emitted from a light-emitting element 1605 is emitted fromboth sides through both the first electrode layer 1617 and the secondelectrode layer 1620.

A display device of FIG. 10 has a structure for top emission in adirection of an arrow. The display device shown in FIG. 10 includes anelement substrate 1300, a display element 1305, a thin film transistor1355, a thin film transistor 1365, a thin film transistor 1375, a thinfilm transistor 1385, a wiring layer 1324, a first electrode layer 1317,a light-emitting layer 1319, a second electrode layer 1320, a protectivefilm 1321, a filler 1322, a sealant 1332, an insulating film 1301 a, aninsulating film 1301 b, a gate insulating layer 1310, an insulating film1311, an insulating film 1312, an insulating layer 1314, a sealingsubstrate 1325, a wiring layer 1333, a terminal electrode layer 1381, ananisotropic conductive layer 1382, and an FPC 1383.

In each of the display devices in FIGS. 10 and 11, an insulating layerstacked over the terminal electrode layer is removed by etching. Whenthe display device has a structure in which an insulating layer havingmoisture permeability is not provided in the vicinity of a terminalelectrode layer, reliability is improved. The display device of FIG. 10includes an external terminal connection region 232, a sealing region233, a peripheral driver circuit region 234, and a pixel region 236. Inthe display device of FIG. 10, the wiring layer 1324 that is a metallayer having reflectivity is formed below the first electrode layer 1317in the display device having a dual emission structure shown in FIG. 11.The first electrode layer 1317 that is a transparent conductive film isformed over the wiring layer 1324. Since it is acceptable as long as thewiring layer 1324 has reflectivity, the wiring layer 1324 may be formedusing a conductive film made of titanium, tungsten, nickel, gold,platinum, silver, copper, tantalum, molybdenum, aluminum, magnesium,calcium, lithium, or an alloy thereof. It is preferable to use asubstance having reflectivity in a visible light range, and a titaniumnitride film is used in this embodiment mode. In addition, the firstelectrode layer 1317 may be formed using a conductive film, and in thatcase, the wiring layer 1324 having reflectivity may be omitted.

Each of the first electrode layer 1317 and the second electrode layer1320 may be formed using a transparent conductive film made of aconductive material having a light-transmitting property, specifically,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. It is needless to say thatindium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide towhich silicon oxide is added (ITSO), or the like can also be used.

Even in a case of using a material such as a metal film which does nothave a light-transmitting property, light can be transmitted through thesecond electrode layer 1320 by forming the second electrode layer 1320very thin preferably, a thickness of approximately 5 nm to 30 nm) so asto be able to transmit light. A metal thin film which can be used as thesecond electrode layer 1320 is a conductive film made of titanium,tungsten, nickel, gold, platinum, silver, aluminum, magnesium, calcium,lithium, or an alloy thereof.

Each pixel of the display device formed using the light-emitting elementcan be driven by a simple matrix mode or an active matrix mode.Furthermore, either a digital drive or an analog drive may be employed.

A sealing substrate may be provided with a color filter (colored layer).The color filter (colored layer) can be formed by an evaporation methodor a droplet discharge method. When the color filter (colored layer) isused, high-definition display can also be performed. This is becausebroad peaks of emission spectra of R, Q and B can be corrected to sharppeaks by the color filter (colored layer).

Full color display can be achieved by using a material exhibitingmonochromatic light emission in combination with a color filter or acolor conversion layer. For example, the color filter (colored layer) orthe color conversion layer may be formed over the sealing substrate andthen attached to the element substrate.

Naturally, display with monochromatic light emission may be performed.For instance, an area-color display device using monochromatic lightemission may be formed. A passive-matrix display portion is suitable forthe area-color display device, and characters and symbols can be mainlydisplayed thereon.

In this embodiment mode, a plurality of pyramidal projections that areadjacent to each other are provided, and a refractive index of theprojection is made to change by a physical pyramidal shape from asurface side of a display screen to the outer side (air side), so thatreflection of light is prevented. Since the display device shown in FIG.11 has a dual-emission structure, light is emitted through both theelement substrate 1600 and the sealing substrate 1625.

Therefore, a viewer side is on each of the element substrate 1600 sideand the sealing substrate 1625 side. Thus, a light-transmittingsubstrate is used as each of the element substrate 1600 and the sealingsubstrate 1625, and the pyramidal projections 1627 a and 1627 b areprovided on respective outer sides that correspond to viewer sides. Inaddition, the pyramidal projections 1627 a and 1627 b are covered withfilms 1628 a and 1628 b each having a higher refractive index than thepyramidal projections 1627 a and 1627 b.

The display device of the present invention is acceptable as long as ithas a pyramidal projection covered with a film. The pyramidal projectionmay be directly formed to have a single continuous structure over asurface of a film (substrate). For example, the surface of the film(substrate) is processed, and the pyramidal projection may be formedthereover, or the film (substrate) may be selectively formed to have apyramidal projection by a printing method such as nanoimprinting.Alternatively, the pyramidal projection may be formed over the film(substrate) in another step.

The plurality of pyramidal projections may be a single continuous filmor be independently arranged over the substrate. Further alternatively,the pyramidal projections may be formed on the substrate in advance.FIG. 10 shows an example in which the plurality of pyramidal projections1327 are provided over a surface of the sealing substrate 1325 as asingle continuous structure.

The display device of this embodiment mode includes a plurality ofpyramidal projections formed over its surface. Light from external isreflected not to a viewer side but to an adjacent pyramidal projectionbecause the surface of each projection is not flat with respect to thedisplay screen. Incident light from external is partly transmittedthrough each pyramidal projection, whereas reflected light is incidenton an adjacent pyramidal projection. In this manner, light reflected ata surface of the pyramidal projections repeats incidence betweenadjacent pyramidal projections.

In other words, the number of times of incidence on the pyramidalprojections among light from external is increased; therefore, theamount of light transmitted through the pyramidal projections isincreased. Thus, the amount of light from external which is reflected toa viewer side is reduced, and the cause of a reduction in visibilitysuch as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented. Since reflection ofincident light from external to the viewer side caused by the flatportions can be reduced, the degree of freedom for selection of shape,setting for arrangement, and a manufacturing process of the pyramidalprojections can be increased.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

In the present invention, in the case where the film and the pyramidalprojection have a large difference in reflactive index, it is preferablethat the thickness of the film be thin.

The pyramidal projection preferably has a side surface with the infinitenumber of normal directions like a conical shape because light can bescattered in multidirection effectively, and accordingly, anantireflection function can be improved. Even in a case of a structurein which flat portions are peovided between the pyramidal projectionslike a conical shape, light incident on the flat portions is reduced dueto the light confinement effect inside the pyramidal projection by thefilm, and reflection to the viewer side can be further prevented.

The pyramidal projection may have a conical shape, a polygonal pyramid(such as a triangular pyramid, quadrangular pyramid, pentagonal pyramid,or six-sided pyramid) shape, a needle-like shape, a shape of aprojection with its apex cut off by a plane parallel to its base, a domeshape with a rounded top, or the like.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projection can be enhanced and reliability isimproved. When conductivity is imparted by selecting a material of thefilm, other effective functions such as a function of prevention ofstatic electricity can be imparted. As a material that can be used forthe film, conductive titanium oxide having a high light-transmittingproperty in visible light; silicon nitride, silicon oxide, or aluminumoxide having high physical strength; aluminum nitride having high heatconductivity; or the like can be used.

For the film, a material with a higher refractive index than at least amaterial used for the pyramidal projection may be used. Accordingly, amaterial used for the film is determined relative to a material of asubstrate for partly constituting a display screen of a display deviceand a material of the pyramidal projection formed over the substrate.Therefore, the material used for the film can be determined asappropriate.

A material used for forming the pyramidal projection and the film may beappropriately selected in accordance with a material of the substratepartly forming a display screen surface, such as silicon, nitrogen,fluorine, oxide, nitride, or fluoride. The oxide may be silicon oxide(SiO₂), boric oxide (B₂O₃), sodium oxide (NaO₂), magnesium oxide (MgO),aluminum oxide (alumina) (Al₂O₃), potassium oxide (K₂O), calcium oxide(CaO), diarsenic trioxide (arsenious oxide) (As₂O₃), strontium oxide(SrO), antimony oxide (Sb₂O₃), barium oxide (BaO), indium tin oxide(ITO), zinc oxide (ZnO), indium zinc oxide (IZO) in which indium oxideis mixed with zinc oxide (ZnO), a conductive material in which indiumoxide is mixed with silicon oxide (SiO₂), organic indium, organic tin,indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like. The nitride may be aluminumnitride (AlN), silicon nitride (SiN), or the like. The fluoride may belithium fluoride (LiF), sodium fluoride (NaF), magnesium fluoride(MgF₂), calcium fluoride (CaF₂), lanthanum fluoride (LaF₃), or the like.The pyramidal projection and the film may include one or more kinds ofthe above-mentioned silicon, nitrogen, fluorine, oxide, nitride, andfluoride. A mixing ratio thereof may be appropriately set in accordancewith a ratio of components (a composition ratio) of the substrate.

The plurality of pyramidal projections and films can be formed byforming a thin film by a sputtering method, a vacuum evaporation method,a PVD (physical vapor deposition) method, or a CVD (chemical vapordeposition) method such as a low-pressure CVD (LPCVD) method or a plasmaCVD method and then etching the thin film into a desired shape.Alternatively, a droplet discharge method by which a pattern can beformed selectively, a printing method by which a pattern can betransferred or drawn (a method for forming a pattern such as screenprinting or offset printing), a coating method such as a spin coatingmethod, a dipping method, a dispenser method, or the like can beemployed. Still alternatively, an imprinting technique or ananoimprinting technique with which a nanoscale three-dimensionalstructure can be formed by a transfer technology can be employed.Imprinting and nanoimprinting are techniques with which a minutethree-dimensional structure can be formed without using aphotolithography process.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 7

This embodiment mode describes an example of a display device having anantireflection function that can further reduce reflection of light fromexternal, for the purpose of providing excellent visibility.Specifically, this embodiment mode describes a light-emitting displaydevice using a light-emitting element as a display element.

This embodiment mode describes a structure of a light-emitting elementwhich can be employed as a display element of the display device of thepresent invention, with reference to FIGS. 22A to 22D.

FIGS. 22A to 22D each show an element structure of a light-emittingelement. In the light-emitting element, an electroluminescent layer 860,in which an organic compound and an inorganic compound are mixed, isinterposed between a first electrode layer 870 and a second electrodelayer 850. The electroluminescent layer 860 includes a first layer 804,a second layer 803, and a third layer 802 as shown, and in particular,the first layer 804 and the third layer 802 are highly characteristic.

The first layer 804 is a layer which functions to transport holes to thesecond layer 803, and includes at least a first organic compound and afirst inorganic compound showing an electron-accepting property to thefirst organic compound. What is important is that the first organiccompound and the first inorganic compound are not only simply mixed, butthe first inorganic compound shows an electron-accepting property to thefirst organic compound. This structure generates many holes carriers inthe first organic compound, which originally has almost no inherentcarriers, and thus, a highly excellent hole-injecting property and ahighly excellent hole-transporting property can be obtained.

Therefore, the first layer 804 can have not only an advantageous effectthat is considered to be obtained by mixing an inorganic compound (suchas improvement in heat resistance) but also excellent conductivity(particularly a hole-injecting property and a hole-transporting propertyin the first layer 804). This excellent conductivity is an advantageouseffect that cannot be obtained in a conventional hole-transporting layerin which an organic compound and an inorganic compound, which do notelectronically interact with each other, are simply mixed. Thisadvantageous effect can make a drive voltage lower than a conventionalone. In addition, since the first layer 804 can be made thicker withoutcausing an increase in drive voltage, short circuit of the element dueto dust and the like can be suppressed.

It is preferable to use a hole-transporting organic compound as thefirst organic compound because holes carriers are generated in the firstorganic compound as described above. Examples of the hole-transportingorganic compound include, but are not limited to, phthalocyanine (abbr.:H₂Pc), copper phthalocyanine (abbr.: CuPc), vanadyl phthalocyanine(abbr.: VOPc), 4,4′,4′-tris(N,N-diphenylamino)triphenylamine (abbr.:TDATA), 4,4′,4′-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbr.: MTDATA), 1,3,5-tris[N,N-di(i-tolyl)amino]benzene (abbr.:m-MTDAB),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(abbr.: TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbr.:NPB), 4,4′-bis{N-[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl(abbr.: DNTPD), 4,4′,4′-tris(N-carbazolyl)triphenylamine (abbr.: TCTA),and the like. In addition, among the compounds mentioned above, aromaticamine compounds as typified by TDATA, MTDATA, m-MTDAB, TPD, NPB, DNTPD,and TCTA can easily generate holes (carriers), and are a suitable groupof compounds for the first organic compound.

On the other hand, the first inorganic compound may be any material aslong as the material can easily accept electrons from the first organiccompound, and various kinds of metal oxides and metal nitrides can beused. An oxide of a transition metal that belongs to any of Groups 4 to12 of the periodic table is preferable because such an oxide of atransition metal easily shows an electron-accepting property.Specifically, titanium oxide, zirconium oxide, vanadium oxide,molybdenum oxide, tungsten oxide, rhenium oxide, ruthenium oxide, zincoxide, or the like can be used. In addition, among the metal oxidesmentioned above, oxides of transition metals that belong to any ofGroups 4 to 8 have a higher electron-accepting property, which are apreferable group of compounds. In particular, vanadium oxide, molybdenumoxide, tungsten oxide, and rhenium oxide are preferable since they canbe formed by vacuum evaporation and can be easily handled.

Note that the first layer 804 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound as described above, or may further include anotherorganic compound or another inorganic compound.

Next, the third layer 802 is described. The third layer 802 is a layerwhich functions to transport electrons to the second layer 803, andincludes at least a third organic compound and a third inorganiccompound showing an electron-donating property to the third organiccompound. What is important is that the third organic compound and thethird inorganic compound are not only simply mixed but also the thirdinorganic compound shows an electron-donating property to the thirdorganic compound. This structure generates many electrons carriers inthe third organic compound which has originally almost no inherentcarriers, and a highly excellent electron-injecting property and ahighly excellent electron-transporting property can be obtained.

Therefore, the third layer 802 can have not only an advantageous effectthat is considered to be obtained by mixing an inorganic compound (suchas improvement in heat resistance) but also excellent conductivity(particularly an electron-injecting property and anelectron-transporting property in the third layer 802). This excellentconductivity is an advantageous effect that cannot be obtained in aconventional electron-transporting layer in which an organic compoundand an inorganic compound, which do not electronically interact witheach other, are simply mixed. This advantageous effect can make a drivevoltage lower than the conventional one. In addition, since the thirdlayer 802 can be made thick without causing an increase in drivevoltage, short circuit of the element due to dust and the like can besuppressed.

It is preferable to use an electron-transporting organic compound as thethird organic compound because electrons carriers are generated in thethird organic compound as described above. Examples of theelectron-transporting organic compound include, but are not limited to,tris(8-quinolinolato)aluminum (abbr.: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbr.: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbr.: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbr.: BAlq),bis[2-(2′-hydroxyphenyl)benzoxazolato]zinc (abbr.: Zn(BOX)₂),bis[2-(2′-hydroxyphenyl)benzothiazolato]zinc (abbr.: Zn(BTZ)₂),bathophenanthroline (abbr.: BPhen), bathocuproin (abbr.: BCP),2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbr.: PBD),1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbr.:OXD-7), 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbr.: TPBI),3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbr.:TAZ),3-4-biphenylyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(abbr.: p-EtTAZ), and the like. In addition, among the compoundsmentioned above, chelate metal complexes each having a chelate ligandincluding an aromatic ring as typified by Alq₃, Amq₃, BeBq₂, BAlq,Zn(BOX)₂, Zn(BTZ)₂, and the like; organic compounds each having aphenanthroline skeleton as typified by BPhen, BCP, and the like; andorganic compounds having an oxadiazole skeleton as typified by PBD,OXD-7, and the like can easily generate electrons (carriers), and aresuitable groups of compounds for the third organic compound.

On the other hand, the third inorganic compound may be any material aslong as the material can easily donate electrons to the third organiccompound, and various kinds of metal oxide and metal nitride can beused. Alkali metal oxide, alkaline earth metal oxide, rare earth metaloxide, alkali metal nitride, alkaline earth metal nitride, and rareearth metal nitride are preferable because they easily show anelectron-donating property. Specifically, lithium oxide, strontiumoxide, barium oxide, erbium oxide, lithium nitride, magnesium nitride,calcium nitride, yttrium nitride, lanthanum nitride, and the like can beused. In particular, lithium oxide, barium oxide, lithium nitride,magnesium nitride, and calcium nitride are preferable because they canbe formed by vacuum evaporation and can be easily handled.

Note that the third layer 802 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound as described above, or may further include anotherorganic compound or another inorganic compound.

Next, the second layer 803 is described. The second layer 803 is a layerwhich functions to emit light, and includes a second organic compoundthat has a light-emitting property. A second inorganic compound may alsobe included. The second layer 803 can be formed by using variouslight-emitting organic compounds and inorganic compounds. However, sinceit is believed to be hard to make a current flow through the secondlayer 803 as compared with the first layer 804 or the third layer 802,the thickness of the second layer 803 is preferably approximately 10 nmto 100 nm.

The second organic compound is not particularly limited as long as it isa light-emitting organic compound, and examples of the second organiccompound include, for example, 9,10-di(2-naphthyl)anthracene (abbr.:DNA), 9,10-di(2-naphthyl)-2-tert-butylanthracene (abbr.: t-BuDNA),4,4′-bis(2,2-diphenylvinyl)biphenyl (abbr.: DPVBi), coumarin 30,coumarin 6, coumarin 545, coumarin 545T, perylene, rubrene,periflanthene, 2,5,8,11-tetra(tert-butyl)perylene (abbr.: TBP),9,10-diphenylanthracene (abbr.: DPA), 5,12-diphenyltetracene,4-(dicyanomethylene)-2-methyl-[p-(dimethylamino)styryl]-4H-pyran (abbr.:DCM1),4-(dicyanomethylene)-2-methyl-6-[2-(julolidine-9-yl)ethenyl]-4H-pyran(abbr.: DCM2),4-(dicyanomethylene)-2,6-his[p-(dimethylamino)styryl]-4H-pyran (abbr.:BisDCM), and the like. In addition, it is also possible to use acompound capable of generating phosphorescence such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(picolinate)(abbr.: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(picolinate)(abbr.: Ir(CF₃ppy)₂(pic)), tris(2-phenylpyridinato-N,C^(2′))iridium(abbr.: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(acetylacetonate) (abbr.:Ir(PPy)₂(acac)),bis[2-(2′-thienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate) (abbr.:Ir(thp)₂(acac)),bis(2-phenylquinolinato-N,C^(2′))iridium(acetylacetonate) (abbr.:Ir(pq)₂(acac)), orbis[2-(2′-benzothienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate)(abbr.: Ir(btp)₂(acac)).

A triplet excitation light-emitting material containing a metal complexor the like may be used for the second layer 803 in addition to asinglet excitation light-emitting material. For example, among pixelsemitting red, green, and blue light, the pixel emitting red light whoseluminance is reduced by half in a relatively short time is formed byusing a triplet excitation light-emitting material and the other pixelsare formed by using a singlet excitation light-emitting material. Atriplet excitation light-emitting material has a feature of favorablelight-emitting efficiency and less power consumption to obtain the sameluminance. In other words, when a triplet excitation light-emittingmaterial is used for a red pixel, only a small amount of current needsto be applied to a light-emitting element, and thus, reliability can beimproved. A pixel emitting red light and a pixel emitting green lightmay be formed using a triplet excitation light-emitting material and apixel emitting blue light may be formed using a singlet excitationlight-emitting material to reduce power consumption. Power consumptioncan be further reduced by forming a light-emitting element which emitsgreen light that is highly visible to human eyes by using a tripletexcitation light-emitting material.

The second layer 803 may include not only the second organic compound asdescribed above, which produces light emission, but also another organiccompound. Examples of organic compounds that can be added include, butare not limited to, TDATA, MTDATA, m-MTDAB, TPD, NPB, DNTPD, TCTA, Alq₃,Almq₃, BeBq₂, BAlq, Zn(BOX)₂, Zn(BTZ)₂, BPhen, BCP, PBD, OXD-7, TPBI,TAZ, p-EtTAZ, DNA, t-BuDNA, and DPVBi, which are mentioned above, andfurther, 4,4′-bis(N-carbazolyl)biphenyl (abbr.: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbr.: TCPB), and the like.It is preferable that the organic compound, which is added in additionto the second organic compound, have higher excitation energy than thesecond organic compound and be added in larger amounts than that of thesecond organic compound in order to make the second organic compoundemit light efficiently (which makes it possible to prevent concentrationquenching of the second organic compound). Alternatively, as anotherfunction, the added organic compound may emit light along with thesecond organic compound (which makes it possible to emit white light orthe like).

The second layer 803 may have a structure in which light-emitting layershaving different light emission wavelength bands are each formed inpixels so as to perform color display. Typically, light-emitting layerscorresponding to respective luminescent colors of R (red), G (green),and B (blue) are formed. In this case, color purity can be improved andspecular surface (reflection) of a pixel portion can be prevented byproviding a filter that transmits light of a certain light emissionwavelength band on a light emission side of the pixels. By providing thefilter, a circular polarizing plate or the like, which has beenconventionally thought to be required, can be omitted, thereby reducingloss of light emitted from the light-emitting layers. In addition, achange in hue, which is caused in the case where a pixel portion (adisplay screen) is seen obliquely, can be reduced.

The material which can be used for the second layer 803 is preferableeither a low-molecular organic light-emitting material or a highmolecular organic light-emitting material. A high molecular organiclight-emitting material has high physical strength in comparison with alow molecular material, and a durability of an element is high. Inaddition, manufacturing of an element is relatively easy because a highmolecular organic light-emitting material can be formed by coating.

Since the color of light is determined by a material of thelight-emitting layer, a light-emitting element that emits light of adesired color can be formed by selecting the material. As the highmolecular electroluminescent material that can be used to form thelight-emitting layer, a polyparaphenylene vinylene based material, apolyparaphenylene based material, a polythiophene based material, or apolyfluorene based material can be given.

As the polyparaphenylene vinylene based material, a derivative ofpoly(paraphenylenevinylene) [PPV]:poly(2,5-dialkoxy-1,4-phenylenevinylene) [RO-PPV];poly[2-(2′-ethyl-hexoxy)-5-methoxy-1,4-phenylenevinylene] [MEH-PPV];poly[2-(dialkoxyphenyl)-1,4-phenylenevinylene] [ROPh-PPV]; or the likecan be used. As the polyparaphenylene based material, a derivative ofpolyparaphenylene [PPP]; poly(2,5-dialkoxy-1,4-phenylene) [RO-PPP];poly(2,5-dihexoxy-1,4-phenylene); or the like can be used. As thepolythiophene based material, a derivative of polythiophene [PT]:poly(3-alkylthiophene) [PAT]; poly(3-hexylthiophene) [PHT];poly(3-cyclohexylthiophene) [PCHT]; poly(3-cyclohexyl-4-methylthiophene)[PCHMT]; poly(3,4-dicyclohexylthiophene) [PDCHT];poly[3-(4-octylphenyl)-thiophene] [POPT];poly[3-(4-octylphenyl)-2,2-bithiophene] [PTOPT]; or the like can beused. As the polyfluorene based material, a derivative of polyfluorene[PF]: poly(9,9-dialkylfluorene) [PDAF]; poly(9,9-dioctylfluorene)[PDOF]; or the like can be given.

The second inorganic compound may be any inorganic compound as long asthe inorganic compound does not easily quench light emission of thesecond organic compound, and various kinds of metal oxide and metalnitride can be used. In particular, an oxide of a metal that belongs toGroup 13 or 14 of the periodic table is preferable because lightemission of the second organic compound is not easily quenched by suchan oxide, and specifically, aluminum oxide, gallium oxide, siliconoxide, and germanium oxide are preferable. However, the second inorganiccompound is not limited thereto.

Note that the second layer 803 may be formed by stacking a plurality oflayers each including a combination of the organic compound and theinorganic compound as described above, or may further include anotherorganic compound or another inorganic compound. A layer structure of thelight-emitting layer can be changed, and an electrode layer forinjecting electrons may be provided or a light-emitting material may bedispersed, instead of providing a specific electron-injecting region orlight-emitting region. Such a change can be permitted unless it departsfrom the spirit of the present invention.

A light-emitting element formed using the above-described material emitslight when biased forwardly. A pixel of a display device formed with thelight-emitting element can be driven by a simple matrix mode or anactive matrix mode. In either mode, each pixel is made to emit light byapplying a forward bias thereto in specific timing, and the pixel is ina non-light-emitting state for a certain period. By applying a reversebias at this non-light-emitting time, reliability of the light-emittingelement can be improved. In the light-emitting element, there is adeterioration mode in which emission intensity is decreased underspecific driving conditions or a deterioration mode in which anon-light-emitting region is enlarged in the pixel and luminance isapparently decreased. However, progression of deterioration can beslowed down by alternating driving. Thus, reliability of thelight-emitting display device can be improved. Either a digital drive oran analog drive can be employed.

Thus, a color filter (colored layer) may be formed over a sealingsubstrate. The color filter (colored layer) can be formed by anevaporation method or a droplet discharge method. When the color filter(colored layer) is used, high-definition display can also be performed.This is because broad peaks of the emission spectra of R, Q and B can becorrected to sharp peaks by the color filter (colored layer).

Full color display can be achieved by forming a material exhibitingmonochromatic light emission in combination with a color filter or acolor conversion layer. For example, the color filter (colored layer) orthe color conversion layer may be formed over the sealing substrate andthen attached to the element substrate.

Naturally, display with monochromatic light emission may be performed.For instance, an area-color display device using monochromatic lightemission may be formed. A passive-matrix display portion is suitable forthe area-color display device, and characters and symbols can be mainlydisplayed thereon.

Materials of the first electrode layer 870 and the second electrodelayer 850 need to be selected considering the work function. The firstelectrode layer 870 and the second electrode layer 850 can be either ananode or a cathode depending on the pixel structure. In the case wherepolarity of a driving thin film transistor is a p-channel type, thefirst electrode layer 870 may serve as an anode and the second electrodelayer 850 may serve as a cathode as shown in FIG. 22A. In the case wherepolarity of the driving thin film transistor is an n-channel type, thefirst electrode layer 870 may serve as a cathode and the secondelectrode layer 850 may serve as an anode as shown in FIG. 22B.Materials that can be used for the first electrode layer 870 and thesecond electrode layer 850 is described. It is preferable to use amaterial having a higher work function (specifically, a material havinga work function of 4.5 eV or higher) for one of the first electrodelayer 870 and the second electrode layer 850, which serves as an anode,and a material having a lower work function (specifically, a materialhaving a work function of 3.5 eV or lower) for the other electrode layerwhich serves as a cathode. However, since the first layer 804 issuperior in a hole-injecting property and a hole-transporting propertyand the third layer 802 is superior in an electron-injecting propertyand an electron transporting property, both of the first electrode layer870 and the second electrode layer 850 are scarcely restricted by a workfunction, and various materials can be used.

Each of the light-emitting elements shown in FIGS. 22A and 22B has astructure in which light is extracted through the first electrode layer870, and thus, the second electrode layer 850 does not necessarily needto have a light-transmitting property. The second electrode layer 850may be formed of a film mainly including an element selected from Ti,Ni, W, Cr, Pt, Zn, Sn, In, Ta, Al, Cu, Au, Ag, Mg, Ca, Li, or Mo, or analloy material or compound material containing the element as its maincomponent such as titanium nitride, TiSi_(X)N_(Y), WSi_(X), tungstennitride, WSi_(X)N_(Y), NbN or a stacked film thereof with a totalthickness ranging from 100 nm to 800 nm.

The second electrode layer 850 can be formed by an evaporation method, asputtering method, a CVD method, a printing method, a dispenser method,a droplet discharge method, or the like.

In addition, when the second electrode layer 850 is formed using alight-transmitting conductive material, like the material used for thefirst electrode layer 870, light is also extracted through the secondelectrode layer 850, and a dual emission structure can be obtained, inwhich light emitted from the light-emitting element is emitted to bothof the first electrode layer 870 side and the second electrode layer 850side.

Note that the light-emitting element according to the present inventionhas many variations by changing types of the first electrode layer 870and the second electrode layer 850.

FIG. 22B shows a case where the third layer 802, the second layer 803,and the first layer 804 are provided in this order from the firstelectrode layer 870 side in the electroluminescent layer 860.

As described above, in the light-emitting element of the presentinvention, a layer interposed between the first electrode layer 870 andthe second electrode layer 850 is formed from the electroluminescentlayer 860 including a layer in which an organic compound and aninorganic compound are combined. The light-emitting element is anorganic-inorganic composite light-emitting element provided with layers(that is, the first layer 804 and the third layer 802) that providefunctions such as a high carrier-injecting property and acarrier-transporting property by mixing an organic compound and aninorganic compound where the functions are not obtainable with eitherthe organic compound or the inorganic compound. Further, the first layer804 and the third layer 802 need to be layers in which an organiccompound and an inorganic compound are combined, particularly whenprovided on the first electrode layer 870 side, and may contain only oneof an organic compound and an inorganic compound when provided on thesecond electrode layer 850 side.

Further, various known methods can be used as a method for forming theelectroluminescent layer 860, which is a layer in which an organiccompound and an inorganic compound are mixed. For example, the methodsinclude a co-evaporation method of evaporating both an organic compoundand an inorganic compound by resistance heating. In addition, forco-evaporation, an inorganic compound may be evaporated by an electronbeam (EB) while evaporating an organic compound by resistance heating.Further, the methods also include a method of sputtering an inorganiccompound while evaporating an organic compound by resistance heating todeposit the both at the same time. In addition, the electroluminescentlayer may also be formed by a wet process.

Similarly, the first electrode layer 870 and the second electrode layer850 can be formed by evaporation by resistance heating, EB evaporation,sputtering, a wet process, and the like.

In FIG. 22C, an electrode layer having reflectivity is used for thefirst electrode layer 870, and an electrode layer having alight-transmitting property is used for the second electrode layer 850in the structure of FIG. 22A. Light emitted from the light-emittingelement is reflected by the first electrode layer 870, then, transmittedthrough the second electrode layer 850, and is emitted to the outside.Similarly, in FIG. 22D, an electrode layer having reflectivity is usedfor the first electrode layer 870, and an electrode layer having alight-transmitting property is used for the second electrode layer 850in the structure of FIG. 22B. Light emitted from the light-emittingelement is reflected by the first electrode layer 870, then, transmittedthrough the second electrode layer 850, and is emitted to the outside.

In the display device of this embodiment mode, a plurality of pyramidalprojections are provided over a surface of a display screen, and thepyramidal projections are each covered with a film with a higherrefractive index than the pyramidal projections. Accordingly, the numberof times of incidence on the pyramidal projections among incident lightfrom external is increased; therefore, the amount of light transmittedthrough the pyramidal projections is increased. Thus, the amount oflight that is reflected to a viewer side is reduced, and the cause of areduction in visibility such as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projections can be enhanced, and reliabilityis improved. When conductivity is imparted by selecting a material ofthe film, other effective functions such as a function of prevention ofstatic electricity can be imparted.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be combined with Embodiment Modes 1 to 3, 5,and 6 as appropriate.

Embodiment Mode 8

This embodiment mode describes an example of a display device having anantireflection function that can further reduce reflection of light fromexternal, for the purpose of providing excellent visibility.Specifically, this embodiment mode describes a light-emitting displaydevice using a light-emitting element as a display element. Thisembodiment mode describes a structure of a light-emitting element whichcan be applied as a display element of the display device of the presentinvention, with reference to FIGS. 23A to 24C.

Light-emitting elements utilizing electroluminescence are classifiedaccording to whether a light-emitting material is an organic compound oran inorganic compound. In general, the former is referred to as anorganic EL element, and the latter is referred to as an inorganic ELelement.

The inorganic EL elements are classified according to their elementstructures into a dispersed inorganic EL element and a thin-filminorganic EL element. They are different in that the former includes anelectroluminescent layer in which particles of a light-emitting materialare dispersed in a binder and the latter includes an electroluminescentlayer formed of a thin film of a light-emitting material; however, theyare common in that they require electrons accelerated by a high electricfield. Note that a mechanism for obtainable light emission includes adonor-acceptor recombination light emission which utilizes a donor leveland an acceptor level and a localized light emission which utilizesinner-shell electron transition of metal ions. In general, it is oftenthe case that the dispersed inorganic EL element performs thedonor-acceptor recombination light emission and the thin-film inorganicEL element performs the localized light emission.

A light-emitting material which can be used in the present inventionincludes a base material and an impurity element serving as alight-emitting center. Light emission of various colors can be obtainedby changing impurity elements to be contained. As a method for producinga light-emitting material, various methods such as a solid phase methodand a liquid phase method (coprecipitation method) can be used. Inaddition, a liquid phase method such as a spray pyrolysis method, adouble decomposition method, a method by precursor pyrolysis, a reversemicelle method, a combined method of one of these methods andhigh-temperature baking, or a freeze-drying method can be used.

The solid phase method is a method by which a base material and animpurity element or a compound containing an impurity element areweighed, mixed in a mortar, and reacted by heating and baking in anelectric furnace to make the impurity element contained in the basematerial. The baking temperature is preferably in the range of 700° C.to 1500° C. This is because solid phase reaction does not proceed whenthe temperature is too low and the base material is decomposed when thetemperature is too high. Note that the baking may be performed in powderform, but the baking is preferably performed in pellet form. The methodrequires baking at a relatively high temperature; however, it is asimple method. Therefore, the method provides good productivity and issuitable for mass production.

The liquid phase method (coprecipitation method) is a method by which abase material or a compound containing a base material is reacted in asolution with an impurity element or a compound containing an impurityelement and the reactant is baked after being dried. Particles of thelight-emitting material are uniformly distributed, a particle size issmall, and the reaction proceeds even at a low baking temperature.

As the base material used for a light-emitting material, sulfide, oxide,or nitride can be used. As sulfide, zinc sulfide (ZnS), cadmium sulfide(CdS), calcium sulfide (CaS), yttrium sulfide (Y₂S₃), gallium sulfide(Ga₂S₃), strontium sulfide (SrS), barium sulfide (BaS), or the like canbe used, for example. As oxide, zinc oxide (ZnO), yttrium oxide (Y₂O₃),or the like can be used, for example. As nitride, aluminum nitride(AlN), gallium nitride (GaN), indium nitride (InN), or the like can beused, for example. Further, zinc selenide (ZnSe), zinc telluride (ZnTe),or the like can also be used. It may be a ternary mixed crystal such ascalcium gallium sulfide (CaGa₂S₄), strontium gallium sulfide (SrGa₂S₄),or barium gallium sulfide (BaGa₂S₄).

As the light-emitting center of localized light emission, manganese(Mn), copper (Cu), samarium (Sm), terbium (Tb), erbium (Er), thulium(Tm), europium (Eu), cerium (Ce), praseodymium (Pr), or the like can beused. Note that a halogen element such as fluorine (F) or chlorine (Cl)may be added. A halogen element can also function as a chargecompensation.

On the other hand, as the light-emitting center of donor-acceptorrecombination light emission, a light-emitting material which contains afirst impurity element forming a donor level and a second impurityelement forming an acceptor level can be used. As the first impurityelement, fluorine (F), chlorine (Cl), aluminum (Al), or the like can beused, for example. As the second impurity element, copper (Cu), silver(Ag), or the like can be used, for example.

In a case of synthesizing the light-emitting material of donor-acceptorrecombination light emission by a solid phase method, a base material, afirst impurity element or a compound containing a first impurityelement, and a second impurity element or a compound containing a secondimpurity element are separately weighed, mixed in a mortar, and thenheated and baked in an electric furnace. As the base material, theabove-mentioned base material can be used. As the first impurity elementor the compound containing the first impurity element, fluorine (F),chlorine (Cl), aluminum sulfate (Al₂S₃), or the like can be used, forexample. As the second impurity element or the compound containing thesecond impurity element, copper (Cu), silver (Ag), copper sulfide(Cu₂S), silver sulfide (Ag₂S), or the like can be used, for example. Thebaking temperature is preferably in the range of 700° C. to 1500° C.This is because solid phase reaction does not proceed when thetemperature is too low and the base material is decomposed when thetemperature is too high. Note that the baking may be performed in powderform, but the baking is preferably performed in pellet form.

As the impurity element in the case of utilizing solid phase reaction, acompound including the first impurity element and the second impurityelement may be used. In this case, the impurity element is easilydiffused and the solid phase reaction easily proceeds, so that a uniformlight-emitting material can be obtained. Furthermore, a high-puritylight-emitting material can be obtained because an unnecessary impurityelement is not mixed. As the compound including the first impurityelement and the second impurity element, copper chloride (CuCl), silverchloride (Agcl), or the like can be used, for example.

Note that the concentration of the impurity element to the base materialmay be in the range of 0.01 atomic % to 10 atomic %, preferably 0.05atomic % to 5 atomic %.

In the case of the thin-film inorganic EL element, theelectroluminescent layer is a layer containing the above-describedlight-emitting material, which can be formed by a vacuum evaporationmethod such as a resistance heating evaporation method or an electronbeam evaporation (EB evaporation) method, a physical vapor deposition(PVD) method such as a sputtering method, a chemical vapor deposition(CVD) method such as a metal organic CVD method or a low-pressurehydride transport CVD method, an atomic layer epitaxy (ALE) method, orthe like.

FIGS. 23A to 23C show examples of a thin-film inorganic EL element whichcan be used as a light-emitting element. In each of FIGS. 23A to 23C, alight-emitting element includes a first electrode layer 50, anelectroluminescent layer 52, and a second electrode layer 53.

Each of the light-emitting elements shown in FIGS. 23B and 23C has astructure in which an insulating layer is provided between the electrodelayer and the electroluminescent layer in the light-emitting element inFIG. 23A. The light-emitting element shown in FIG. 23B includes aninsulating layer 54 between the first electrode layer 50 and theelectroluminescent layer 52. The light-emitting element shown in FIG.23C includes an insulating layer 54 a between the first electrode layer50 and the electroluminescent layer 52 and an insulating layer 54 bbetween the second electrode layer 53 and the electroluminescent layer52. As described above, the insulating layer may be provided between theelectroluminescent layer and either or both of the pair of electrodelayers sandwiching the electroluminescent layer. The insulating layermay be a single layer or a stack of a plurality of layers.

In FIG. 23B, the insulating layer 54 is provided in contact with thefirst electrode layer 50. However, the insulating layer 54 may beprovided in contact with the second electrode layer 53 by reversing theorder of the insulating layer and the electroluminescent layer.

In the case of the dispersed inorganic EL element, a particulatelight-emitting material is dispersed in a binder to form a film-likeelectroluminescent layer. In a case where a particle having a desiredsize cannot be sufficiently obtained by a production method of alight-emitting material, the material may be processed into particles bycrushing in a mortar or the like. The binder is a substance for fixing aparticulate light-emitting material in a dispersed manner and holdingthe material in shape as the electroluminescent layer. Thelight-emitting material is uniformly dispersed and fixed in theelectroluminescent layer by the binder.

In the case of the dispersed inorganic EL element, theelectroluminescent layer can be formed by a droplet discharge methodwhich can selectively form the electroluminescent layer, a printingmethod (such as screen printing or off-set printing), a coating methodsuch as a spin-coating method, a dipping method, a dispenser method, orthe like. The thickness is not particularly limited, but it ispreferably in the range of 10 nm to 1000 nm. In addition, in theelectroluminescent layer containing the light-emitting material and thebinder, the proportion of the light-emitting material is preferably inthe range of 50 wt % to 80 wt %.

FIGS. 24A to 24C show examples of a dispersed inorganic EL element whichcan be used as a light-emitting element. A light-emitting element inFIG. 24A has a stacked structure of a first electrode layer 60, anelectroluminescent layer 62, and a second electrode layer 63, andcontains a light-emitting material 61 held by a binder in theelectroluminescent layer 62.

As the binder which can be used in this embodiment mode, an insulatingmaterial can be used, such as an organic insulating material, aninorganic insulating material, or a mixed material of an organicinsulating material and an inorganic insulating material can be used. Asan organic insulating material, a polymer having a relatively highdielectric constant, such as a cyanoethyl cellulose resin, or a resinsuch as polyethylene, polypropylene, a polystyrene resin, a siliconeresin, an epoxy resin, or vinylidene fluoride can be used.Alternatively, a heat resistant high molecular compound such as aromaticpolyamide or polybenzimidazole, or a siloxane resin may be used. Notethat the siloxane resin corresponds to a resin including Si—O—Si bonds.Siloxane includes a skeleton formed from a bond of silicon (Si) andoxygen (O). An organic group containing at least hydrogen (for example,an alkyl group or aromatic hydrocarbon) or a fluoro group may be usedfor a substituent, or an organic group containing at least hydrogen anda fluoro group may be used for substituents. Alternatively, a resinmaterial such as a vinyl resin like polyvinyl alcohol orpolyvinylbutyral, a phenol resin, a novolac resin, an acrylic resin, amelamine resin, a urethane resin, or an oxazole resin (polybenzoxazole)may be used. A dielectric constant can be adjusted by appropriatelymixing high dielectric constant fine particles of barium titanate(BaTiO₃), strontium titanate (SrTiO₃), or the like in the above resin.

As an inorganic insulating material included in the binder, a materialselected from substances containing inorganic insulating materials canbe used, such as silicon oxide (SiO_(X)), silicon nitride (SiN_(X)),silicon containing oxygen and nitrogen, aluminum nitride (AlN), aluminumcontaining oxygen and nitrogen, aluminum oxide (Al₂O₃), titanium oxide(TiO₂), BaTiO₃, SrTiO₃, lead titanate (PbTiO₃), potassium niobate(KNbO₃), lead niobate (PbNbO₃), tantalum oxide (Ta₂O₅), barium tantalate(BaTa₂O₆), lithium tantalate (LiTaO₃), yttrium oxide (Y₂O₃), orzirconium oxide (ZrO₂). A dielectric constant of the electroluminescentlayer including the light-emitting material and the binder can becontrolled by making an organic material containing a high dielectricconstant inorganic insulating material (by addition or the like), sothat a dielectric constant can be increased. When a mixed layer of aninorganic material and an organic material is used as a binder to obtainhigh dielectric constant, a higher electric charge can be induced in thelight-emitting material.

In a producing process, a light-emitting material is dispersed in asolution including a binder. As a solvent of the solution including thebinder that can be used in this embodiment mode, a solvent in which abinder material is soluble and which can produce a solution having aviscosity suitable for a method for forming the electroluminescent layer(various wet processes) and a desired thickness, may be selectedappropriately. An organic solvent or the like can be used. In the caseof using, for example, a siloxane resin as the binder, propylene glycolmonomethyl ether, propylene glycol monomethyl ether acetate (alsoreferred to as PGMEA), 3-methoxy-3-methyl-1-butanol (also referred to asMMB), or the like can be used.

Each of the light-emitting elements shown in FIGS. 2413 and 24C has astructure in which an insulating layer is provided between the electrodelayer and the electroluminescent layer in the light-emitting element inFIG. 24A. The light-emitting element shown in FIG. 24B includes aninsulating layer 64 between the first electrode layer 60 and theelectroluminescent layer 62. The light-emitting element shown in FIG.24C includes an insulating layer 64 a between the first electrode layer60 and the electroluminescent layer 62 and an insulating layer 64 bbetween the second electrode layer 63 and the electroluminescent layer62. As described above, the insulating layer may be provided between theelectroluminescent layer and either or both of the pair of electrodessandwiching the electroluminescent layer. In addition, the insulatinglayer may be a single layer or a stack of a plurality of layers.

In FIG. 24B, the insulating layer 64 is provided in contact with thefirst electrode layer 60. However, the insulating layer 64 may beprovided in contact with the second electrode layer 63 by reversing theorder of the insulating layer and the electroluminescent layer.

An insulating layer such as the insulating layer 54 in FIGS. 23A to 23Cor the insulating layer 64 in FIGS. 24A to 24C is not particularlylimited, but it preferably has high withstand voltage and dense filmquality. Furthermore, it preferably has a high dielectric constant. Forexample, a film of silicon oxide (SiO₂), yttrium oxide (Y₂O₃), titaniumoxide (TiO₂), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), tantalumoxide (Ta₂O₅), barium titanate (BaTiO₃), strontium titanate (SrTiO₃),lead titanate (PbTiO₃), silicon nitride (Si₃N₄), zirconium oxide (ZrO₂),or the like, a mixed film thereof or a stacked film of two or more kindscan be used. These insulating films can be formed by sputtering,evaporation, CVD, or the like. Alternatively, the insulating layer maybe formed by dispersing particles of the insulating material in abinder. A binder material may be formed using a material and a methodsimilar to those of the binder included in the electroluminescent layer.The thickness is not particularly limited, but it is preferably in therange of 10 nm to 1000 nm.

The light-emitting element described in this embodiment mode, which canprovide light emission by applying voltage between a pair of electrodelayers sandwiching the electroluminescent layer, can be operated byeither DC drive or AC drive.

In the display device of this embodiment mode, a plurality of pyramidalprojections are provided over a surface of a display screen, and thepyramidal projections are covered with film having a higher refractiveindex than the pyramidal projections. Accordingly, the number of timesof incidence on the pyramidal projections among light from external thatis incident on the display device is increased and, the amount of lighttransmitted through the pyramidal projections is increased. Thus, theamount of light reflected to a viewer side is reduced, and the cause ofa reduction in visibility such as reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projections can be enhanced, and reliabilityis improved. When conductivity is imparted by selecting a material ofthe film, other effective functions such as a function of prevention ofstatic electricity can be imparted.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be combined with Embodiment Modes 1 to 3, 5,and 6 as appropriate.

Embodiment Mode 9

This embodiment mode describes a structure of a backlight. A backlightis provided in a display device as a backlight unit having a lightsource. In the backlight unit, the light source is surrounded by areflector plate so that light is scattered efficiently.

As shown in FIG. 16A, a cold cathode tube 401 can be used as a lightsource in a backlight unit 352. In order to reflect light efficiently bythe cold cathode tube 401, a lamp reflector 332 can be provided. Thecold cathode tube 401 is mostly used for a large-sized display devicedue to the intensity of the luminance from the cold cathode tube.Therefore, the backlight unit having a cold cathode tube can be used fora display of a personal computer.

As shown in FIG. 16B, a light-emitting diode (LED) 402 can be used as alight source in the backlight unit 352. For example, light-emittingdiodes (W) 402 emitting light of a white color are arranged withpredetermined intervals. In order to reflect light efficiently by thelight-emitting diode (W) 402, the lamp reflector 332 can be provided.

As shown in FIG. 16C, light-emitting diodes (LED) 403, 404, and 405emitting light of colors of RGB can be used as a light source in thebacklight unit 352. When the light-emitting diodes (LED) 403, 404, and405 emitting light of colors of RGB are used, color reproducibility canbe enhanced as compared with a case when only the light-emitting diode(W) 402 emitting light of a white color is used. In order to reflectlight efficiently by the light emission diodes, the lamp reflector 332can be provided.

As shown in FIG. 16D, when light-emitting diodes (LED) 403, 404, and 405emitting light of colors of RGB is used as a light source, it is notnecessary that the number and arrangement thereof are the same for all.For example, a plurality of light-emitting diodes emitting light of acolor that has low light-emitting intensity (such as green) may bearranged.

Furthermore, the light-emitting diode 402 emitting light of a whitecolor and the light-emitting diodes (LED) 403, 404, and 405 emittinglight of colors of RGB may be combined.

When a field sequential mode is applied in a case of using thelight-emitting diodes of RGB, color display can be performed bysequentially lighting the light-emitting diodes of ROB in accordancewith the time.

The light-emitting diode is suitable for a large-sized display devicebecause the luminance thereof is high. In addition, colorreproducibility of the light-emitting diode is superior to that of acold cathode tube because the color purity of each color of RGB isfavorable, and an area required for arrangement can be reduced.Therefore, a narrower frame can be achieved when the light-emittingdiode is applied to a small-sized display device.

Further, a light source does not need to be provided as the backlightunits shown in FIGS. 16A to 16D. For example, when a backlight having alight-emitting diode is mounted on a large-sized display device, thelight-emitting diode can be arranged on the back side of the substrate.In this case, each of the light-emitting diodes can be sequentiallyarranged with predetermined intervals. Color reproducibility can beenhanced in accordance with the arrangement of the light-emittingdiodes.

By providing a display device using such a backlight with a plurality ofpyramidal projections covered with a film having a higher refractiveindex than the pyramidal projections over its surface, a high-visibilitydisplay device can have a high antireflection function that can furtherreduce reflection of light from external. Accordingly, a morehigh-quality and high-performance display device can be manufactured. Abacklight having a light-emitting diode is particularly suitable for alarge-sized display device, and a high-quality image can be providedeven in a dark place by enhancing the contrast ratio of the large-sizeddisplay device.

This embodiment mode can be combined with any of Embodiment Modes 1 to 4as appropriate.

Embodiment Mode 10

FIG. 15 shows an example of forming an EL display module manufactured byapplying the present invention. In FIG. 15, a pixel portion includingpixels is formed over a substrate 2800. A flexible substrate is used aseach of the substrate 2800 and a sealing substrate 2820.

In FIG. 15, a TFT which has a similar structure to that formed in thepixel, or a protective circuit portion 2801 operated in a similar mannerto a diode by connecting a gate to either a source or a drain of the TFTis provided between a driver circuit and the pixel and outside the pixelportion. A driver IC formed of a single crystalline semiconductor, astick driver IC formed of a polycrystalline semiconductor film over aglass substrate, a driver circuit formed of a SAS, or the like isapplied to a driver circuit 2809.

The substrate 2800 provided with an element layer is fixed to thesealing substrate 2820 with spacers 2806 a and 2806 b formed by adroplet discharge method interposed therebetween. The spacers arepreferably provided to keep a distance between two substrates constanteven when the substrate is thin or an area of the pixel portion isenlarged. A space between the substrate 2800 and the sealing substrate2820 over light-emitting elements 2804 and 2805 connected to TFTs 2802and 2803 respectively may be filled with a light-transmitting resinmaterial and the resin material may be solidified, or may be filled withanhydrous nitrogen or an inert gas. Pyramidal projections 2827 areprovided on an outer side of the sealing substrate 2820 whichcorresponds to a viewer side, and films 2828 are formed to cover thepyramidal projections 2827.

FIG. 15 shows a case where the light-emitting elements 2804 and 2805have a top-emission structure, in which light is emitted in thedirection of arrows shown in the drawing. Multicolor display can beperformed by making the pixels emit light of different colors of red,green, and blue. At this time, color purity of the light emitted outsidecan be improved by forming colored layers 2807 a to 2807 c correspondingto respective colors on the sealing substrate 2820 side. Moreover,pixels which emit white light may be used and may be combined with thecolored layers 2807 a to 2807 c.

The driver circuit 2809 which is an external circuit is connected by awiring board 2810 to a scan line or signal-line connection terminalwhich is provided at one end of an external circuit substrate 2811. Inaddition, a heat pipe 2813, which is a high-efficiency heat conductiondevice having a pipe-like shape, and a heat sink 2812 may be provided incontact with or adjacent to the substrate 2800 to enhance a heatdissipation effect.

Note that FIG. 15 shows the top-emission EL module; however, a bottomemission structure may be employed by changing the structure of thelight-emitting element or the disposition of the external circuit board.Naturally, a dual emission structure in which light is emitted from boththe top and bottom surfaces may be used. In the case of the top emissionstructure, the insulating layer serving as a partition may be coloredand used as a black matrix. This partition can be formed by a dropletdischarge method and it may be formed by mixing a black resin of apigment material, carbon black, or the like into a resin material suchas polyimide. A stack thereof may alternatively be used.

In addition, reflected light of light which is incident from the outerside may be blocked by using a retardation plate or a polarizing plate.An insulating layer serving as a partition may be colored and used as ablack matrix. This partition can be formed by a droplet dischargemethod. Carbon black or the like may be mixed into a resin material suchas polyimide, and a stack thereof may also be used. By a dropletdischarge method, different materials may be discharged to the sameregion plural times to form the partition. A quarter-wave plate or ahalf-wave plate may be used as the retardation plate and may be designedto be able to control light. As the structure, a TFT element substrate,the light-emitting element, the sealing substrate (sealant), theretardation plate (quarter-wave plate or a half-wave plate), and thepolarizing plate are sequentially stacked, through which light emittedfrom the light-emitting element is transmitted and emitted outside fromthe polarizing plate side. The retardation plate or polarizing plate maybe provided on a side where light is emitted or may be provided on bothsides in the case of a dual emission display device in which light isemitted from the both surfaces. In addition, a plurality of pyramidalprojections may be provided on the outer side of the polarizing plate.Accordingly, a more high-definition and accurate image can be displayed.

In this embodiment mode, the plurality of pyramidal projections aredensely provided over a substrate to a viewer side. A sealing structuremay be formed on a side opposite to the viewer side with the elementinterposed therebetween, in which a resin film is attached to the sidewhere the pixel portion is formed, with the use of a sealant or anadhesive resin. Various sealing methods such as resin sealing using aresin, plastic sealing using plastic, and film sealing using a film canbe used. A gas barrier film which prevents water vapor from penetratingthe resin film is preferably provided over the surface of the resinfilm. By employing a film sealing structure, further reductions inthickness and weight can be achieved.

In the display device of this embodiment mode, a plurality of pyramidalprojections are provided over a surface of a display screen, and thepyramidal projections are each covered with a film with a higherrefractive index than the pyramidal projections. Accordingly, the numberof times of incidence on the pyramidal projections among light fromexternal which is incident on the display device is increased;therefore, the amount of light transmitted through the pyramidalprojections is increased. Thus, the amount of light reflected to aviewer side is reduced, and the cause of a reduction in visibility suchas reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident tight on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projections can be enhanced, and reliabilityis improved. When conductivity is imparted by selecting a material ofthe film, other effective functions such as a function of prevention ofstatic electricity can be imparted.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be combined with Embodiment Modes 1 to 3, 5,and 8 as appropriate.

Embodiment Mode 11

This embodiment mode is described with reference to FIGS. 14A and 14B.FIGS. 14A and 14B show examples of forming a display device (liquidcrystal display module) by using a TFT substrate 2600 manufactured inaccordance with the present invention.

FIG. 14A shows an example of a liquid crystal display module, in whichthe TFT substrate 2600 and an opposite substrate 2601 are fixed to eachother with a sealant 2602, and a pixel portion 2603 including a TFT, adisplay element 2604 including a liquid crystal layer, a colored layer2605, and a polarizing plate 2606 are provided between the substrates toform a display region. The colored layer 2605 is necessary to performcolor display. In the case of the RGB system, respective colored layerscorresponding to colors of red, green, and blue are provided forrespective pixels. A polarizing plate 2607 and a diffuser plate 2613 areprovided on an outer side of substrate 2600. A polarizing plate 2606 isprovided on an inner side of opposite substrate 2601. Pyramidalprojections 2626 and films 2627 are provided on an outer side ofopposite substrate 2601. A light source includes a cold cathode tube2610 and a reflector plate 2611. A circuit board 2612 is connected tothe TFT substrate 2600 by a flexible wiring board 2609. Externalcircuits such as a control circuit and a power supply circuit areincorporated in the circuit board 2612. Reference numeral 2608 denotes adriver circuit. The polarizing plate and the liquid crystal layer may bestacked with a retardation plate interposed therebetween. In thisembodiment mode, the films 2627 are formed to cover the pyramidalprojections 2626.

The display device in FIG. 14A is an example in which the pyramidalprojections 2626 are provided on an outer side of the opposite substrate2601, and the polarizing plate 2606 and the colored layer 2605 aresequentially provided on an inner side. However, the polarizing plate2606 may be provided on the outer side of the opposite substrate 2601(to a viewer side), and in that case, the pyramidal projections 2626 maybe provided over a surface of the polarizing plate 2606. The stackedstructure of the polarizing plate 2606 and the colored layer 2605 isalso not limited to that shown in FIG. 14A and may be appropriately setdepending on materials of the polarizing plate 2606 and the coloredlayer 2605 or conditions of manufacturing steps.

The liquid crystal display module can employ a TN (Twisted Nematic)mode, an IPS (In-Plane-Switching) mode, an FFS (Fringe Field Switching)mode, an MVA (Multi-domain Vertical Alignment) mode, a PVA (PatternedVertical Alignment) mode, an ASM (Axially Symmetric aligned Micro-cell)mode, an OCB (Optical Compensated Birefringence) mode, an FLC(Ferroelectric Liquid Crystal) mode, an AFLC (Anti Ferroelectric LiquidCrystal) mode, or the like.

FIG. 14B shows an example of applying an OCB mode to the liquid crystaldisplay module of FIG. 14A, so that this liquid crystal display moduleis an FS-LCD (Field Sequential-LCD). The FS-LCD performs red, green, andblue light emissions in one frame period. Color display can be performedby composing an image by a time division method. Also, emission of eachcolor is performed using a light-emitting diode, a cold cathode tube, orthe like; hence, a color filter is not required. There is no necessityfor arranging color filters of three primary colors and limiting adisplay region of each color. Display of all three colors can beperformed in any region. On the other hand, light emission of threecolors is performed in one frame period; therefore, high speed responseof liquid crystal is needed. When an FLC mode using an FS system and theOCB mode are applied to the display device of this embodiment mode inthe present invention, a display device or a liquid crystal televisiondevice having higher performance and high image quality can becompleted.

A liquid crystal layer of the OCB mode has, what is called, a π cellstructure. In the π cell structure, liquid crystal molecules areoriented such that pretilt angles of the molecules are symmetrical withrespect to the center plane between the active matrix substrate and theopposite substrate. The orientation in the π cell structure is a splayorientation when a voltage is not applied between the substrates, andshifts into a bend orientation when the voltage is applied. Whitedisplay is performed in this bend orientation. Further voltageapplication makes the liquid crystal molecules in the bend orientationorientated perpendicular to the substrates, which does not allow lightto pass therethrough. Note that a response speed approximately ten timesas high as that of a conventional TN mode can be achieved by using theOCB mode.

Further, as a mode corresponding to the FS system, an HV(Half V)-FLC, anSS(Surface Stabilized)-FLC, or the like using a ferroelectric liquidcrystal (FLC) that can be operated at high speed can also be used. Anematic liquid crystal that has relatively low viscosity can be used forthe OCB mode. A smectic liquid crystal that has a ferroelectric phasecan be used for the HV-FLC or the SS-FLC.

An optical response speed of the liquid crystal display module isincreased by narrowing a cell gap of the liquid crystal display module.Alternatively, the optical response speed can be increased by loweringthe viscosity of the liquid crystal material. The above method ofincreasing the optical response speed is more effective when a pixelpitch of a pixel region of a TN-mode liquid crystal display module is 30μm or less. The optical response speed can be further increased by anoverdrive method in which an applied voltage is increased (or decreased)only for a moment.

The liquid crystal display module of FIG. 14B is a transmissive liquidcrystal display module, in which a red light source 2910 a, a greenlight source 2910 b, and a blue light source 2910 c are provided aslight sources. A control portion 2912 is provided in the liquid crystaldisplay module to separately control the red light source 2910 a, thegreen light source 2910 b, and the blue light source 2910 c to be turnedon or off. The light emission of each color is controlled by the controlportion 2912, and light enters the liquid crystal to compose an imageusing the time division, thereby performing color display.

In the display device of this embodiment mode, a plurality of pyramidalprojections are provided over a display screen surface, and thepyramidal projections are each covered with a film with a higherrefractive index than the pyramidal projections. Accordingly, the numberof times of incidence on the pyramidal projections among light fromexternal which is incident on the display device is increased;therefore, the amount of light transmitted through the pyramidalprojections is increased. Thus, the amount of light reflected to aviewer side is reduced, and the cause of a reduction in visibility suchas reflection can be eliminated.

When light is incident from a material with a high refractive index to amaterial with a low refractive index, a large difference in refractiveindex easily causes total reflection of light. When surfaces of thepyramidal projections are each covered with a film having a highrefractive index, among light going toward the outer side of thepyramidal projections, light reflected inside the pyramidal projectionsat interfaces between the films and air is increased. Furthermore, thetravelling direction of light inside the pyramidal projections becomescloser to a direction perpendicular to a bottom due to refraction oflight at interfaces between the films and the pyramidal projection, andlight is incident on the bottom (display screen); therefore, the numberof times of reflection inside the pyramidal projections is decreased.Accordingly, by covering each pyramidal projection with a film having ahigh refractive index, the light confinement effect in the pyramidalprojections is improved, and reflection to the outer side of thepyramidal projections can be reduced.

Even when the pyramidal projections are adjacent with intervals and haveflat portions therebetween, reflection of light to a viewer side causedby the flat portions can be prevented because reflection to the outerside of the pyramidal projections can be prevented.

By stacking a pyramidal projection and a film having a difference inrefractive index, there is an effect that among incident light on thefilm and pyramidal projection, optical interfere is generated betweenreflected light at an interface between air and the film and reflectedlight at an interface between the film and the pyramidal projection, sothat reflected light is reduced.

By covering the pyramidal projection with the film, the physicalstrength of the pyramidal projections can be enhanced, and reliabilityis improved. When conductivity is imparted by selecting a material ofthe film, other effective functions such as a function of prevention ofstatic electricity can be imparted.

In this embodiment mode, a high-visibility display device can beprovided, which has a plurality of pyramidal projection formed over itssurface and a high antireflection function that can further reduce lightfrom external by covering films having a higher refractive index thanthe pyramidal projections. Accordingly, a display device with higherimage quality and a higher performance can be provided.

This embodiment mode can be combined with Embodiment Modes 1 to 4 and 9as appropriate.

Embodiment Mode 12

With the display device formed by the present invention, a televisiondevice (also referred to as simply a television, or a televisionreceiver) can be completed. FIG. 19 is a block diagram showing maincomponents of the television device.

FIG. 17A is a top view showing a structure of a display panel accordingto the present invention. A pixel portion 2701 in which pixels 2702 arearranged in matrix, a scan line input terminal 2703, and a signal lineinput terminal 2704 are formed over a substrate 2700 having aninsulating surface. The number of pixels may be determined in accordancewith various standards. In a case of XGA full-color display using RGB,the number of pixels may be 1024×768×3 (RGB). In a case of UXGAfull-color display using RGB, the number of pixels may be 1600×1200×3(RGB), and in a case of full-spec, high-definition, and full-colordisplay using RGB, the number may be 1920×1080×3 (RGB).

The pixels 2702 are formed in matrix by intersections of scan linesextended from the scan line input terminal 2703 and signal linesextended from the signal line input terminal 2704. Each pixel 2702 inthe pixel portion 2701 is provided with a switching element and a pixelelectrode layer connected thereto. A typical example of the switchingelement is a TFT. A gate electrode layer of the TFT is connected to thescan line, and a source or a drain of the TFT is connected to the signalline, which enables each pixel to be independently controlled by asignal inputted from the outside.

FIG. 17A shows a structure of a display panel in which a signal to beinputted to the scan line and the signal line is controlled by anexternal driver circuit. Alternatively, a driver IC 2751 may be mountedon the substrate 2700 by a COG (Chip on Glass) method as shown in FIG.18A. As another mounting mode, a TAB (Tape Automated Bonding) method maybe used as shown in FIG. 1811. The driver IC may be formed over a singlecrystalline semiconductor substrate or may be formed using a TIT over aglass substrate. In each of FIGS. 18A and 18B, the driver IC 2751 isconnected to an FPC (Flexible Printed Circuit) 2750.

When a TFT provided in a pixel is formed of a crystalline semiconductor,a scan line driver circuit 3702 can be formed over a substrate 3700 asshown in FIG. 17B. In FIG. 17B, a pixel portion 3701 is controlled by anexternal driver circuit connected to a signal line input terminal 3704,similarly to FIG. 17A. When the TFT provided in a pixel is formed of apolycrystalline (microcrystalline) semiconductor, a single crystallinesemiconductor, or the like having high mobility, a pixel portion 4701, ascan-line driver circuit 4702, and a signal-line driver circuit 4704 canall be formed over a glass substrate 4700 as shown in FIG. 17C.

As for the display panel, there are the following cases: a case in whichonly a pixel portion 901 is formed as shown in FIG. 17A and a scan linedriver circuit 903 and a signal line driver circuit 902 are mounted by aTAB method as shown in FIG. 18B; a case in which the scan line drivercircuit 903 and the signal line driver circuit 902 are mounted by a COGmethod as shown in FIG. 18A; a case in which a TFT is formed as shown inFIG. 171, the pixel portion 901 and the scan line driver circuit 903 areformed over a substrate, and the signal line driver circuit 902 isseparately mounted as a driver IC; a case in which the pixel portion901, the signal line driver circuit 902, and the scan line drivercircuit 903 are formed over a substrate as shown in FIG. 17C; and thelike. The display panel may have any of the structures.

As another external circuit in FIG. 19, a video signal amplifier circuit905 which amplifies a video signal among signals received by a tuner904, a video signal processing circuit 906 which converts the signalsoutputted from the video signal amplifier circuit 905 into chrominancesignals corresponding to respective colors of red, green, and blue, acontrol circuit 907 which converts the video signal into an inputspecification of the driver IC, and the like are provided on an inputside of the video signal. The control circuit 907 outputs signals toboth a scan line side and a signal line side. In the case of digitaldrive, a signal dividing circuit 908 may be provided on the signal lineside and an input digital signal may be divided into in pieces andsupplied.

An audio signal among signals received by the tuner 904 is sent to anaudio signal amplifier circuit 909 and is supplied to a speaker 913through an audio signal processing circuit 910. A control circuit 911receives control information of a receiving station (receptionfrequency) or sound volume from an input portion 912 and transmitssignals to the tuner 904 and the audio signal processing circuit 910.

A television device can be completed by incorporating the display moduleinto a chassis as shown in FIGS. 20A and 20B. When a liquid crystaldisplay module is used as a display module, a liquid crystal televisiondevice can be manufactured. When an EL display module is used, an ELtelevision device can be manufactured. In FIG. 20A, a main screen 2003is formed by using the display module, and a speaker portion 2009, anoperation switch, and the like are provided as its accessory equipment.Thus, a television device can be completed in accordance with thepresent invention.

A display panel 2002 is incorporated in a chassis 2001, and general TVbroadcast can be received by a receiver 2005. When the display device isconnected to a communication network by wired or wireless connectionsvia a modem 2004, one-way (from a sender to a receiver) or two-way(between a sender and a receiver or between receivers) informationcommunication can be performed. The television device can be operated byusing a switch built in the chassis 2001 or a remote control unit 2006.A display portion 2007 for displaying output information may also beprovided in the remote control device 2006.

Further, the television device may include a sub screen 2008 formedusing a second display panel so as to display channels, volume, or thelike, in addition to the main screen 2003. In this structure, both themain screen 2003 and the sub screen 2008 can be formed using the liquidcrystal display panel of the present invention. Alternatively, the mainscreen 2003 may be formed using an Ft display panel having a wideviewing angle, and the sub screen 2008 may be formed using a liquidcrystal display panel capable of displaying images with less powerconsumption. In order to reduce the power consumption preferentially,the main screen 2003 may be formed using a liquid crystal display panel,and the sub screen may be formed using an EL display panel, which can beswitched on and off. In accordance with the present invention, ahigh-reliability display device can be formed even when a large-sizedsubstrate is used and a large number of TFTs or electronic componentsare used.

FIG. 20B shows a television device having a large-sized display portion,for example, a 20-inch to 80-inch display portion. The television deviceincludes a chassis 2010, a display portion 2011, a remote control device2012 that is an operation portion, a speaker portion 2013, and the like.This embodiment mode of the present invention is applied tomanufacturing of the display portion 2011. Since the television devicein FIG. 20B is a wall-hanging type, it does not require a largeinstallation space.

Naturally, the present invention is not limited to the televisiondevice, and can be applied to various use applications as a large-sizeddisplay medium such as an information display board at a train station,an airport, or the like, or an advertisement display board on thestreet, as well as a monitor of a personal computer.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 11 as appropriate.

Embodiment Mode 13

Examples of electronic devices in accordance with the present inventionare as follows: a television device (also referred to as simply atelevision, or a television receiver), a camera such as a digital cameraor a digital video camera, a cellular telephone device (simply alsoreferred to as a cellular phone or a cell-phone), an informationterminal such as PDA, a portable game machine, a computer monitor, acomputer, a sound reproducing device such as a car audio system, animage reproducing device including a recording medium, such as ahome-use game machine, and the like. Further, the present invention canbe applied to various game machines having a display device such as asling machine, a slot machine, a pinball machine, and a large-scaledgame machine. Preferred modes of them are described with reference toFIGS. 21A to 21F.

A portable information terminal device shown in FIG. 21A includes a mainbody 9201, a display portion 9202, and the like. The display device ofthe present invention can be applied to the display portion 9202. As aresult, a high-performance portable information terminal device whichcan display a high-quality image with high visibility can be provided.

A digital video camera shown in FIG. 21B includes a display portion9701, a display portion 9702, and the like. The display device of thepresent invention can be applied to the display portion 9701. As aresult, a high-performance digital video camera which can display ahigh-quality image with high visibility can be provided.

A cellular phone shown in FIG. 21C includes a main body 9101, a displayportion 9102, and the like. The display device of the present inventioncan be applied to the display portion 9102. As a result, ahigh-performance cellular phone which can display a high-quality imagewith high visibility can be provided.

A portable television device shown in FIG. 21D includes a main body9301, a display portion 9302 and the like. The display device of thepresent invention can be applied to the display portion 9302. As aresult, a high-performance portable television device which can displaya high-quality image with high visibility can be provided. The displaydevice of the present invention can be applied to a wide range oftelevision devices ranging from a small-sized television device mountedon a portable terminal such as a cellular phone, a medium-sizedtelevision device which can be carried, to a large-sized (for example,40-inch or larger) television device.

A portable computer shown in FIG. 21E includes a main body 9401, adisplay portion 9402, and the like. The display device of the presentinvention can be applied to the display portion 9402. As a result, ahigh-performance portable computer which can display a high-qualityimage with high visibility can be provided.

A slot machine shown in FIG. 21F includes a main body 9501, a displayportion 9502, and the like. The display device of the present inventioncan be applied to the display portion 9502. As a result, ahigh-performance slot machine which can display a high-quality imagewith high visibility can be provided.

As described above, a high-performance electronic device which candisplay a high-quality image with high visibility can be provided byusing the display device of the present invention.

This embodiment mode can be freely combined with any of Embodiment Modes1 to 12.

Embodiment 1

This embodiment describes the result of optical measurement of theantireflection model used in the present invention. Further, the opticalmeasurement was also performed for a model including only pyramidalprojections as a comparative example. In this embodiment, the result ofthe optical measurement is described with reference to FIG. 29 and FIGS.32A to 34C.

The optical measurement was performed for a comparative example ofconical projections (refractive index of 1.35) as pyramidal projectionsand conical projections (refractive index of 1.35) each covered with afilm (refractive index of 1.9) (referred to as structures A1 to A4) aspyramidal projections. In the comparative example, a height H1 of thepyramidal projection is 1500 nm, and a width L1 thereof is 300 nm. Ineach of the structures A1 to A4, a height H2 of the film and thepyramidal projection is 1500 n, and a width L2 thereof is 300 nm. Aheight difference d between the top of the pyramidal projection and thetop of the film is 60 nm in the structure A1, 45 nm in the structure A2,40 nm in the structure A3, and 35 nm in the structure A4. The width L1of the pyramidal projection is changed so that the ratio of the heightH1 of the pyramidal projection to the width L1 of the base is constantly1:5. In the structures A1 to A4, the height H1 of the pyramidalprojection is changed to correspond to the height difference d betweenthe top of the pyramidal projection and the top of the film. A pluralityof pyramidal projections each covered with a film are most denselyarranged to be adjacent to each other so that six pyramidal projectionsare in contact with one pyramidal projection through the films.

As for the measurement in this embodiment, an optical measurementsimulator for optical devices, Diffract MOD (manufactured by RsoftDesign Group, Inc.) was used. The reflectivity is measured by opticalmeasurement in three dimensions. FIG. 29 shows each relation ofreflectivity and the wavelength of light in the comparative example andthe structures A1 to A4. As one of measurement conditions, Harmonicsthat is parameter of the above measurement simulator is set at 3 in boththe X direction and Y direction. When each interval between the tops ofpyramidal projections is represented by p, and the height of thepyramidal projection and the film is represented by H2, Index Res. thatis also a parameter of the above measurement simulator is set to be anumeric value obtained by formulas of √{square root over (3)}×p/512 inthe X direction, p/512 in the Y direction, and H2/80 in the Z direction.

In FIG. 29, diamond dots denote the comparative example, square dotsdenote the structure A1, triangle dots denote the structure A2, x-markdots denote the structure A3, and *-mark dots denote the structure A4.FIG. 29 shows each relation of the wavelength and reflectivity. Theoptical measurement can also confirm that at measured wavelengths from380 nm to 780 nm, the reflectivity of the structures A1 to A4, which aremodels of the pyramidal projections covered with films, is lower thanthat of the comparative example, and accordingly, reflectivity can bereduced. Further, in the structures A1 to A4, when differences d ofheight between the top of the pyramidal projection and the top of thefilm are 45 nm (structure A2), 40 nm (structure A3), and 35 nm(structure A4), reflectivity can be further suppressed.

Next, in the models of the pyramidal projections each covered with afilm using the present invention, a refractive index difference Δnbetween the pyramidal projection and the film and the height differenced between the top of the pyramidal projection and the top of the filmare changed, so that change in reflectivity at each wavelength wasmeasured. The refractive index of the pyramidal projection is set to be1.49, and the measurement was performed by changing the refractive indexof the film. The height H2 between the film and the pyramidal projectionis 1500 nm, the width L2 thereof is 300 nm, and the height H1 of thepyramidal projection is changed to correspond to the height difference dbetween the top of the pyramidal projection and the top of the film. Thewidth L1 of the pyramidal projection was changed so that the ratio ofthe height H1 of the pyramidal projection to the width L1 of the base isconstantly 1:5. A plurality of pyramidal projections each covered with afilm have conical shapes and are most densely arranged to be adjacent toeach other, so that six pyramidal projections are in contact with onepyramidal projection through the films.

FIGS. 32A to 32C show change in reflectivity R (%) to a refractive indexdifference Δn between the pyramidal projection and the film when theheight difference d between the top of the pyramidal projection and thetop of the film is changed: 0 nm (black diamond dots), 10 nm (blacksquare dots), 20 nm (black triangle dots), 30 nm (×-mark dots), 40 nm(*-mark dots), 50 nm (black circle dots), 60 nm (cross-mark dots), 70 nm(hollow triangle dots), 80 nm (hollow circle dots), 90 nm (hollowdiamonds dots), and 100 nm (hollow square dots).

FIGS. 33A to 33C show change in reflectivity R (%) to the heightdifference d between the top of the pyramidal projection and the top ofthe film when a refractive index difference Δn between the pyramidalprojection and the film is changed: 0.05 (black diamond dots), 0.35α-mark dots), 0.65 (cross-mark dots), 0.95 (hollow diamond dots), 1.15(black triangle dots), 1.45 (lack circle dots), 1.75 (hollow triangledots), 1.95 (black triangle dots), 2.25 (*-mark dots), and 2.55 (hollowcircle dots). The measurement is performed at a light wavelength of 440nm which exhibits blue visible light (FIGS. 32A and 33A), at a lightwavelength of 550 nm which exhibits green visible light (FIGS. 32B and33B), and at a light wavelength of 620 nm which exhibits red visiblelight (FIGS. 32C and 33C), and then the result is obtained.

In FIGS. 32A to 32C, as the refractive index difference Δn between thepyramidal projection and the film is increased, the reflectivity isincreased. This tendency becomes prominent as the height difference dbetween the top of the pyramidal projection and the top of the film isincreased. In FIGS. 33A to 33C, as the height difference d between thetop of the pyramidal projection and the top of the film is increased,reflectivity is increased. This tendency becomes prominent as therefractive index difference Δn between the pyramidal projection and thefilm is increased.

FIGS. 34A to 34C show relations of the height difference d between thetop of the pyramidal projection and the top of the film, the refractiveindex difference Δn between the pyramidal projection and the film, andreflectivity. In FIGS. 34A to 34C, based on the reflectivity of apyramidal projection not covered with the film as a reference, a regionis denoted by dots where the reference reflectivity is smaller than thatof the pyramidal projection covered with the film having the differenced between the top and the top of the film, whereas a region is denotedby oblique lines where the reference reflectivity is larger than that ofthe pyramidal projection covered with the film having the difference dbetween the top and the top of the film. FIG. 34A is a graph of therelations based on the reflectivity of 0.021% (without film), at a lightwavelength of 400 nm. FIG. 34B is a graph of the relations based on thereflectivity of 0.023% (without film), at a light wavelength of 550 nm.FIG. 34C is a graph of the relations based on the reflectivity of 0.027%(without film), at a light wavelength of 620 nm.

According to the graphs of FIGS. 34A to 34C, in the case where therefractive index difference Δn between the pyramidal projection and thefilm is greater than or equal to 0.05 or more and less than or equal to0.65, if the height difference d between the top of the pyramidalprojection and the top of the film is 100 nm or less, reflectivity canbe suppressed to be lower than the reference reflectivity in the casewhere the film is not formed, which is preferable. According to thegraphs of FIGS. 34A to 34C, in the case where the refractive indexdifference Δn between the pyramidal projection and the film is greaterthan or equal to 0.65 and less than or equal to 1.15, if the heightdifference d between the top of the pyramidal projection and the top ofthe film is 50 nm or less, reflectivity can be suppressed to be lowerthan the reference reflectivity in the case where the film is notformed, which is preferable. Further, the height difference d betweenthe top of the pyramidal projection and the top of the film ispreferably 1 nm or more.

The height difference d between the top of the pyramidal projection andthe top of the film depends on the thickness of the film and is changedsimilarly to change in the thickness. Therefore, the height difference dbetween the top of the pyramidal projection and the top of the film canalso be referred to as the thickness of the film.

The described-above confirmed that in a case where the refractive indexdifference between the film and the pyramidal projection is large, thethickness of the film (the height difference between the top of thepyramidal projection and the top of the film) is preferably thin.

Accordingly, the present invention could confirm that a highantireflection function is obtained by providing a plurality ofpyramidal projections over a surface and covering each pyramidalprojection with a film having a higher refractive index than thepyramidal projections.

This application is based on Japanese Patent Application serial no.2006-327793 filed with Japan Patent Office on Dec. 5, 2006, the entirecontents of which are hereby incorporated by reference.

1. A display device comprising: a pair of substrates; at least a pair ofelectrodes interposed between the pair of substrates; a display elementinterposed between the pair of electrodes; and an antireflection filmprovided over an outer side of one of the pair of substrates, whereinone of the pair of substrates is the light transmitting substrate,wherein the antireflection film has a plurality of pyramidalprojections, wherein the plurality of pyramidal projections are eachcovered with a film, wherein a refractive index of the film is higherthan a refractive index of the pyramidal projection, and wherein aninterval is provided at least between one side of a base included in oneof the pyramidal projections and one side of a base included in anadjacent pyramidal projection.
 2. A display device comprising: a pair ofsubstrates; at least a pair of electrodes interposed between the pair ofsubstrates; a display element interposed between the pair of electrodes;and an antireflection film provided over an outer side of one of thepair of substrates, wherein one of the pair of substrates is the lighttransmitting substrate, wherein the antireflection film has a pluralityof pyramidal projections, wherein the plurality of pyramidal projectionsare each covered with a film, and wherein a refractive index of the filmis higher than a refractive index of the pyramidal projection.
 3. Adisplay device according to claim 1 or 2, wherein a polarizing plate isprovided between the light-transmitting substrate and the plurality ofpyramidal projections.
 4. A display device according to claim 1 or 2,wherein the display element is a light-emitting element.
 5. A displaydevice according to claim 1 or 2, wherein the display element is aliquid crystal display element.
 6. A display device according to claim 1or 2, wherein a refractive index difference between the plurality ofpyramidal projections and the film is greater than or equal to 0.05 andless than or equal to 0.65, and wherein a height difference between atop of the plurality of pyramidal projections and the top of the film is100 nm or less.
 7. A display device according to claim 1 or 2, wherein arefractive index difference between the plurality of pyramidalprojections and the film is greater than or equal to 0.65 and less thanor equal to 1.15, and wherein a height difference between a top of theplurality of pyramidal projections and a top of the film is 50 nm orless.
 8. A display device according to claim 1 or 2, wherein the one ofthe plurality of pyramidal projections is in a conical shape.
 9. Adisplay device according to claim 1 or 2, wherein the one of theplurality of pyramidal projections is in a six-sided pyramid shape. 10.A display device according to claim 1 or 2, wherein the one of theplurality of pyramidal projections is in a quadrangular pyramid.
 11. Adisplay device according to claim 1 or 2, wherein apexes of theplurality of pyramidal projections are arranged at regular intervalsapart from each other.
 12. A display device according to claim 1 or 2,wherein the one of the plurality of pyramidal projections has roundedtop.
 13. A display device according to claim 1 or 2, wherein theantireflection film is a part of the one of the pair of the substrates.14. A display device according to claim 1 or 2, wherein theantireflection film is formed of different layer from the one of thepair of the substrates.
 15. An antireflection film comprising: whereinthe antireflection film has a plurality of pyramidal projections,wherein the plurality of pyramidal projections are each covered with afilm, and wherein a refractive index of the film is higher than arefractive index of the pyramidal projection.
 16. An antireflection filmcomprising: wherein the antireflection film has a plurality of pyramidalprojections, wherein the plurality of pyramidal projections are eachcovered with a film, wherein a refractive index of the film is higherthan a refractive index of the pyramidal projection, and wherein aninterval is provided at least between one side of a base included in oneof the pyramidal projections and one side of a base included in anadjacent pyramidal projection.
 17. An antireflection film according toclaim 15 or 16, wherein a refractive index difference between theplurality of pyramidal projections and the film is greater than or equalto 0.05 and less than or equal to 0.65, and wherein a height differencebetween a top of the plurality of pyramidal projections and the top ofthe film is 100 nm or less.
 18. An antireflection film according toclaim 15 or 16, wherein a refractive index difference between theplurality of pyramidal projections and the film is greater than or equalto 0.65 and less than or equal to 1.15, and wherein a height differencebetween a top of the plurality of pyramidal projections and a top of thefilm is 50 nm or less.
 19. An antireflection film according to claim 15or 16, wherein the one of the plurality of pyramidal projections is in aconical shape.
 20. An antireflection film according to claim 15 or 16,wherein the one of the plurality of pyramidal projections is in asix-sided pyramid shape.
 21. An antireflection film according to claim15 or 16, wherein the one of the plurality of pyramidal projections isin a quadrangular pyramid.
 22. An antireflection film according to claim15 or 16, wherein apexes of the plurality of pyramidal projections arearranged at regular intervals apart from each other.
 23. Anantireflection film according to claim 15 or 16, wherein the one of theplurality of pyramidal projections has rounded top.